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  • 301.
    Streib, Simon
    et al.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Szilva, Attila
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Borisov, Vladislav
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Pereiro, Manuel
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Bergman, Anders
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Sjoqvist, Erik
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Katsnelson, Mikhail, I
    Radboud Univ Nijmegen, Inst Mol & Mat, Heyendaalseweg 135, NL-6525 AJ Nijmegen, Netherlands..
    Eriksson, Olle
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Örebro Univ, Sch Sci & Technol, S-70281 Örebro, Sweden..
    Thonig, Danny
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Örebro Univ, Sch Sci & Technol, S-70281 Örebro, Sweden..
    Exchange constants for local spin Hamiltonians from tight-binding models2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, no 22, article id 224413Article in journal (Refereed)
    Abstract [en]

    We consider the mapping of tight-binding electronic structure theory to a local spin Hamiltonian, based on the adiabatic approximation for spin degrees of freedom in itinerant-electron systems. Local spin Hamiltonians are introduced in order to describe the energy landscape of small magnetic fluctuations, locally around a given spin configuration. They are designed for the linear response near a given magnetic state and, in general, are insufficient to capture arbitrarily strong deviations of spin configurations from the equilibrium. In order to achieve this mapping, we include a linear term in the local spin Hamiltonian that together with the usual bilinear exchange tensor, produces an improved accuracy of effective magnetic Weiss fields for noncollinear states. We also provide examples from tight-binding electronic structure theory, where our implementation of the calculation of exchange constants is based on constraining fields that stabilize an out-of-equilibrium spin configuration. We check our formalism by means of numerical calculations for iron dimers and chains.

  • 302.
    Stålhammar, Marcus
    et al.
    Nordita SU; Department of Physics, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden.
    Rudneva, D.
    Department of Physics, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden.
    Hansson, T. H.
    Department of Physics, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden.
    Wilczek, Frank
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Department of Physics, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden; Center for Theoretical Physics, MIT, Cambridge, Massachusetts 02139, USA; T. D. Lee Institute and Wilczek Quantum Center, Shanghai Jiao Tong University, Shanghai 200240, China; Department of Physics, Arizona State University, Tempe, Arizona 85287, USA.
    Emergent Chern-Simons interactions in 3+1 dimensions2024In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 109, no 6, article id 064514Article in journal (Refereed)
    Abstract [en]

    Parity-violating superconductors can support a low-dimension local interaction that becomes, upon condensation, a purely spatial Chern-Simons term. Solutions to the resulting generalized London equations can be obtained from solutions of the ordinary London equations with a complex penetration depth, and suggest several remarkable physical phenomena. The problem of flux exclusion by a sphere brings in an anapole moment, the problem of current-carrying wires brings in an azimuthal magnetic field, and the problem of vortices brings in currents along the vortices. We demonstrate that interactions of this kind, together with a conceptually related dimensionally reduced Chern-Simons interaction, can arise from physically plausible microscopic interactions.

  • 303.
    Sugiyama, Jun
    et al.
    CROSS Neutron Sci & Technol Ctr, Tokai, Ibaraki 3191106, Japan.;Japan Atom Energy Agcy, Adv Sci Res Ctr, Tokai, Ibaraki 3191195, Japan.;High Energy Accelerator Res Org KEK, Tokai, Ibaraki 3191106, Japan..
    Andreica, Daniel
    Babes Bolyai Univ, Fac Phys, Cluj Napoca 400084, Romania..
    Forslund, Ola Kenji
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Nocerino, Elisabetta
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Matsubara, Nami
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Sassa, Yasmine
    Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden..
    Guguchia, Zurab
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Psi, Switzerland..
    Khasanov, Rustem
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Psi, Switzerland..
    Pratt, Francis L.
    STFC Rutherford Appleton Lab, ISIS Pulsed Neutron & Muon Facil, Didcot OX11 0QX, Oxon, England..
    Nakamura, Hiroyuki
    Kyoto Univ, Dept Mat Sci & Engn, Kyoto 6068501, Japan..
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Magnetic phase boundary of BaVS3 clarified with high-pressure mu+SR2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 17, article id 174403Article in journal (Refereed)
    Abstract [en]

    The magnetic nature of the quasi-one-dimensional BaVS3 has been studied as a function of temperature down to 0.25 K and pressure up to 1.97 GPa on a powder sample using the positive muon spin rotation and relaxation (mu(+) SR) technique. At ambient pressure, BaVS3 enters an incommensurate antiferromagnetic ordered state below the Neel temperature (T-N)31 K. T-N is almost constant as the pressure (p) increases from ambient pressure to 1.4 GPa, then T-N decreases rapidly for p > 1.4 GPa, and finally disappears at p similar to 1.8 GPa, above which a metallic phase is stabilized. Hence, T-N is found to be equivalent to the pressure-induced metal-insulator transition temperature (T-MI) at p > 1.4 GPa.

  • 304.
    Sugiyama, Jun
    et al.
    Comprehens Res Org Sci & Soc CROSS, Neutron Sci & Technol Ctr, Tokai, Ibaraki 3191106, Japan.;Japan Atom Energy Agcy, Adv Sci Res Ctr, Tokai, Ibaraki 3191195, Japan.;High Energy Accelerator Res Org KEK, Tokai, Ibaraki 3191106, Japan..
    Higemoto, Wataru
    Japan Atom Energy Agcy, Adv Sci Res Ctr, Tokai, Ibaraki 3191195, Japan..
    Andreica, Daniel
    Babes Bolyai Univ, Fac Phys, Cluj Napoca 400084, Romania..
    Forslund, Ola Kenji
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Nocerino, Elisabetta
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Sassa, Yasmine
    Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden..
    Gupta, Ritu
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Khasanov, Rustem
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Ohta, Hiroto
    Kyoto Univ, Dept Mat Sci & Engn, Kyoto 6068501, Japan..
    Nakamura, Hiroyuki
    Kyoto Univ, Dept Mat Sci & Engn, Kyoto 6068501, Japan..
    Pressure dependence of ferromagnetic phase boundary in BaVSe3 studied with high-pressure mu+SR2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, no 10, article id 104418Article in journal (Refereed)
    Abstract [en]

    The magnetic nature of a quasi-one-dimensional compound, BaVSe3, has been investigated with positive muon spin rotation and relaxation (mu+SR) measurements at ambient and high pressures. At ambient pressure, the mu+SR spectrum recorded under zero external magnetic field exhibited a clear oscillation below the Curie temperature (T-C similar to 41 K) due to the formation of quasistatic ferromagnetic order. The oscillation consisted of two different muon spin precession signals, indicating the presence of two magnetically different muon sites in the lattice. However, the two precession frequencies, which correspond to the internal magnetic fields at the two muon sites, could not be adequately explained with relatively simple ferromagnetic structures using the muon sites predicted by density functional theory calculations. The detailed analysis of the internal magnetic field suggested that the V moments align ferromagnetically along the c axis but slightly canted toward the a axis by 28 degrees that is coupled antiferromagnetically. The ordered V moment (M-v) is estimated as (0.59, 0, 1.11) mu(B). As pressure increased from ambient pressure, T-C was found to decrease slightly up to about 1.5 GPa, at which point T-C started to increase rapidly with the further increase of the pressure. Based on a strong ferromagnetic interaction along the c axis, the high-pressure mu+SR result revealed that there are two magnetic interactions in the ab plane; one is an antiferromagnetic interaction that is enhanced with pressure, mainly at pressures below 1.5 GPa, while the other is a ferromagnetic interaction that becomes predominant at pressures above 1.5 GPa.

  • 305. Sugiyama, Jun
    et al.
    Nozaki, Hiroshi
    Umegaki, Izumi
    Miwa, Kazutoshi
    Higemoto, Wataru
    Ansaldo, Eduardo J.
    Brewer, Jess H.
    Sakurai, Hiroya
    Isobe, Masahiko
    Takagi, Hidenori
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Magnetism of the A-site ordered perovskites CaCu3Cr4O12 and LaCu3Cr4O122018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 2, article id 024416Article in journal (Refereed)
    Abstract [en]

    The microscopic magnetic nature of the A-site ordered chromium perovskites CaCu3Cr4O12 and LaCu3Cr4O12 and their solid-solution system, Ca1-x LaxCu3Cr4O12, with x = 0.2, 0.4, and 0.8, has been studied with muon spin rotation and relaxation (mu+SR) measurements down to 2 K using a powder sample. For CaCu3Cr4O12, mu+SR revealed the formation of static antiferromagnetic (AF) order below 122 K (=T-N), although magnetization measurements showed a very small change at T-N. Analyses of the internal magnetic field H-int at the muon sites, predicted with first-principles calculations, suggested G-type AF order as a ground state. For LaCu3Cr4O12 with T-N = 225 K, mu+SR also supported the presence of aG-type AF ordered state, which was recently proposed based on neutron diffraction measurements. However, the ordered Cr moments were found to change the direction at around 10 K. For Ca1-xLaxCu3Cr4O12, both T-N and H-int at 2 K increase monotonically with x.

  • 306.
    Sugiyama, Jun
    et al.
    Comprehens Res Org Sci & Soc CROSS, Neutron Sci & Technol Ctr, Tokai, Ibaraki 3191106, Japan.;Japan Atom Energy Agcy, Adv Sci Res Ctr, Tokai, Ibaraki 3191195, Japan.;High Energy Accelerator Res Org KEK, Tokai, Ibaraki 3191106, Japan..
    Umegaki, Izumi
    Toyota Cent Res & Dev Labs Inc, Nagakute, Aichi 4801192, Japan..
    Takeshita, Soshi
    High Energy Accelerator Res Org KEK, Tokai, Ibaraki 3191106, Japan..
    Sakurai, Hiroya
    Natl Inst Mat Sci NIMS, Namiki 1-1, Tsukuba, Ibaraki 3050044, Japan..
    Nishimura, Shoichiro
    High Energy Accelerator Res Org KEK, Tokai, Ibaraki 3191106, Japan..
    Forslund, Ola Kenji
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Nocerino, Elisabetta
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Matsubara, Nami
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Nakano, Takehito
    Ibaraki Univ, Grad Sch Sci & Engn, Inst Quantum Beam Sci, Mito, Ibaraki 3108512, Japan..
    Yamauchi, Ichihiro
    Saga Univ, Grad Sch Sci & Engn, Dept Phys, Saga 8408502, Japan..
    Ninomiya, Kazuhiko
    Osaka Univ, Grad Sch Sci, Dept Chem, Toyonaka, Osaka 5600043, Japan..
    Kubo, M. Kenya
    Int Christian Univ, Coll Liberal Arts, Mitaka, Tokyo 1818585, Japan..
    Shimomura, Koichiro
    High Energy Accelerator Res Org KEK, Tokai, Ibaraki 3191106, Japan..
    Nuclear magnetic field in Na0.7CoO2 detected with mu-SR2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, no 14, article id 144431Article in journal (Refereed)
    Abstract [en]

    The internal magnetic field in a sodium battery compound, i.e., the paramagnet Na0.7CoO2, was investigated with negative muon spin rotation and relaxation (mu-SR), and the result was compared with the results previously obtained with mu+SR. The majority of implanted mu(-) is captured on an oxygen nucleus, while mu(+) locates an interstitial site. Therefore, a mu(+/-) SR work provides information on the internal magnetic field, which is formed by nuclear magnetic moments of Na-23 and Co-59, from the two different viewpoints. Besides a slight decrease in the field distribution width (Delta) around 300 K, the nuclear magnetic field detected with mu- SR was found to be almost static and temperature independent up to 400 K, even though Na ions are known to start to diffuse above 290 K based on mu(+) SR, Na-NMR, neutron scattering, and electrochemical measurements. Such a discrepancy is caused by the fact that the Na contribution to Delta is only about 3% at the O site whereas it is about 13% at the interstitial site, where the mu(+) is presumably located.

  • 307.
    Sukhachov, P. O.
    et al.
    Nordita SU.
    Gorbar, E. , V
    Department of Physics, Taras Shevchenko National Kyiv University, Kyiv 03680, Ukraine ; Bogolyubov Institute for Theoretical Physics, Kyiv 03680, Ukraine.
    Superconductivity in Weyl semimetals in a strong pseudomagnetic field2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, no 1, article id 014513Article in journal (Refereed)
    Abstract [en]

    The superconducting s-wave state in Weyl semimetals in a strong strain-induced pseudomagnetic field is investigated in a model with local four-fermion interaction. It is found that only the internode pairing is possible in the lowest pseudo-Landau level approximation. Unlike the case of the lowest Landau level in a conventional magnetic field, the corresponding gap equation has only a trivial solution. Nevertheless, superconductivity can be induced via the proximity effect with a usual s-wave spin-singlet superconductor. Since a pseudomagnetic field is present necessarily at the surface of a Weyl semimetal, the proximity effect is strongly affected by the pseudomagnetic field. The analysis of such an effect showed that while no gap is opened in the spectrum, the degeneracy of energy levels is lifted. The unique character of the proximity effect in Weyl semimetals can be probed via the density of states, the spectral function, and the tunneling current. The density of states does not vanish at small energies and scales linearly with the pseudomagnetic field strength. This scaling is manifested also in the tunneling current.

  • 308.
    Sukhachov, Pavlo O.
    et al.
    Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden;Nordita SU.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden;Univ Connecticut, Dept Phys, Storrs, CT 06269 USA.
    Spectroscopic and optical response of odd-frequency superconductors2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 13, article id 134516Article in journal (Refereed)
    Abstract [en]

    The optical response of superconductors with odd-frequency Berezinskii pairing is studied. By using a simple model with a parabolic dispersion law and a nonmagnetic disorder, the spectral function, the electron density of states, and the optical conductivity are calculated for a few gap Ansatze. The spectral function and the electron density of states clearly reveal the gap for the Berezinskii pairing for the sufficiently strong frequency dependence of the order parameters. It is found that, similarly to the conventional BCS pairing, the odd-frequency gaps induce peaks in the real part of the conductivity, which, however, are sharper than in the BCS case. The magnitude and position of these peaks are determined by the frequency profile of the gap. The imaginary part of the optical conductivity for the Berezinskii pairing demonstrates sharp cusps that are absent in the case of the BCS superconductors. The corresponding results suggest that the Berezinskii pairing might allow for the optical transparency windows related to the onsets of the attenuation peaks in the real part of the conductivity. Thus, the study of the optical response not only provides an alternative way to probe the odd-frequency gaps, but can also reveal additional features of the dynamic superconducting pairing.

  • 309.
    Sukhachov, Pavlo O.
    et al.
    Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden.;Nordita SU.
    Juricic, Vladimir
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Odd-frequency Berezinskii superconductivity in Dirac semimetals2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 18, article id 180502Article in journal (Refereed)
    Abstract [en]

    We formulate a general framework for addressing both odd- and even-frequency superconductivity in Dirac semimetals and demonstrate that the odd-frequency or the Berezinskii pairing can naturally appear in these materials because of the chirality degree of freedom. We show that repulsive frequency-dependent interactions favor the Berezinskii pairing while an attractive electron-electron interaction allows for the BCS pairing. In the case of Dirac and Weyl semimetals at the charge neutrality point, both the conventional BCS and odd-frequency Berezinskii pairings require critical coupling. Since these pairings could originate from physically different mechanisms, our findings pave the way for controlling the realization of the Berezinskii superconductivity in topological semimetals. We also present the density of states with several cusplike features that can serve as an experimentally verifiable signature of the odd-frequency gap.

  • 310.
    Talkachov, Anton
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Wave functions and edge states in rectangular honeycomb lattices revisited: Nanoflakes, armchair and zigzag nanoribbons, and nanotubes2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 4, article id 045419Article in journal (Refereed)
    Abstract [en]

    Properties of bulk and boundaries of materials can, in general, be quite different, both for topological and nontopological reasons. One of the simplest boundary problems to pose is the tight-binding problem of noninteracting electrons on a finite honeycomb lattice. Despite its simplicity, the problem is quite rich and directly related to the physics of graphene. We revisit this long-studied problem and present an analytical derivation of the electron spectrum and wave functions for graphene rectangular derivatives. We provide an exact analytical description of extended and localized states, the transition between them, and a special case of a localized state when the wave function is nonzero only at the edge sites. The latter state has zero energy, and we discuss its existence in zigzag nanoribbons, zigzag nanotubes with a number of sites along a zigzag edge divisible by 4, and rectangular graphene nanoflakes with an odd number of sites along both zigzag and armchair edges.

  • 311.
    Talkachov, Anton
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Samoilenka, Albert
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Microscopic study of boundary superconducting states on a honeycomb lattice2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, no 13, article id 134507Article in journal (Refereed)
    Abstract [en]

    We address the problem of boundary s-wave superconductivity on rectangular honeycomb lattices: nanoflakes, armchair, and zigzag nanotubes. We discuss how the presence of edges and corners in these systems can significantly alter the superconducting correlations at a macroscopic length scale, leading to either nontrivial enhancement or suppression of the superconducting gap value near the boundaries. This in turn results in different critical temperatures of the gap closure at boundaries compared to the bulk gap. The effects are macroscopic but strongly depend on the atomic-level structure of the boundaries.

  • 312.
    Teixeira, Raphael L. R. C.
    et al.
    Univ Sao Paulo, Inst Fis, CP 66318, BR-05315970 Sao Paulo, SP, Brazil..
    Kuzmanovski, Dushko
    Stockholm Univ, SE-10691 Stockholm, Sweden.;Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Nordita SU.
    Black-Schaffer, Annica M.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Dias da Silva, Luis G. G., V
    Univ Sao Paulo, Inst Fis, CP 66318, BR-05315970 Sao Paulo, SP, Brazil..
    Enhanced Majorana bound states in magnetic chains on superconducting topological insulator edges2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, no 16, article id 165312Article in journal (Refereed)
    Abstract [en]

    The most promising mechanisms for the formation of Majorana bound states (MBSs) in condensed matter systems involve one-dimensional systems [such as semiconductor nanowires, magnetic chains, and quantum spin Hall insulator (QSHI) edges] proximitized to superconducting materials. The choice between each of these options involves tradeoffs between several factors such as reproducibility of results, system tunability, and robustness of the resulting MBS. In this paper, we propose that a combination of two of these systems, namely, a magnetic chain deposited on a QSHI edge in contact with a superconducting surface, offers a better choice of tunability and MBS robustness compared to magnetic chain deposited on bulk. We study how the QSHI edge interacts with the magnetic chain, and see how the topological phase is affected by edge proximity. We show that MBSs near the edge can be realized with lower chemical potential and Zeeman field than the ones inside the bulk, independently of the chain's magnetic order (ferromagnetic or spiral order). Different magnetic orderings in the chain modify the overall phase diagram, even suppressing the boundless topological phase found in the bulk for chains located at the QSHI edge. Moreover, we quantify the "quality" of MBSs by calculating the Majorana polarization (MP) for different configurations. For chains located at the edge, the MP is close to its maximum value already for short chains. For chains located away from the edge, longer chains are needed to attain the same quality as chains located at the edge. The MP also oscillates in phase with the in-gap states, which is relatively unexpected as peaks in the energy spectrum correspond to stronger overlap of MBSs.

  • 313.
    Theveniaut, Hugo
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Vojta, Matthias
    Bound states of fractionalized excitations in a modulated Kitaev spin liquid2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 5, article id 054401Article in journal (Refereed)
    Abstract [en]

    Fractionalization is a hallmark of spin-liquid behavior; it typically leads to response functions consisting of continua instead of sharp modes. However, microscopic processes can enable the formation of short-distance bound states of fractionalized excitations, despite asymptotic deconfinement. Here we study such bound-state formation for the Z(2) spin liquid realized in Kitaev's honeycomb compass model, supplemented by a kekule distortion of the lattice. Bound states between flux pairs andMajorana fermions form in theMajorana band gaps. We calculate the dynamic spin susceptibility and show that bound states lead to sharp modes in the magnetic response of the spin liquid, with the momentum dependence of the corresponding spectral weight encoding the internal symmetry of the bound state. As a byproduct, we also show that isolated fluxes may produce Majorana bound states at exactly zero energy. Generalizations and implications of the results are discussed.

  • 314.
    Thiyam, P.
    et al.
    Lund Univ, Div Theoret Chem, POB 124, SE-22100 Lund, Sweden..
    Parashar, Prachi
    John A Logan Coll, Carterville, IL 62918 USA.;Norwegian Univ Sci & Technol, Dept Energy & Proc Engn, NO-7491 Trondheim, Norway..
    Shajesh, K. , V
    Malyi, O. , I
    Bostrom, M.
    Norwegian Univ Sci & Technol, Dept Energy & Proc Engn, NO-7491 Trondheim, Norway.;Univ Oslo, Ctr Mat Sci & Nanotechnol, POB 1048 Blindern, NO-0316 Oslo, Norway..
    Milton, K. A.
    Univ Oklahoma, Homer L Dodge Dept Phys & Astron, Norman, OK 73019 USA..
    Brevik, I
    Norwegian Univ Sci & Technol, Dept Energy & Proc Engn, NO-7491 Trondheim, Norway..
    Forsman, J.
    Lund Univ, Div Theoret Chem, POB 124, SE-22100 Lund, Sweden..
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Effect of excess charge carriers and fluid medium on the magnitude and sign of the Casimir-Lifshitz torque2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 20, article id 205403Article in journal (Refereed)
    Abstract [en]

    Last year, we reported a perturbative theory of the Casimir-Lifshitz torque between planar biaxially anisotropic materials in the retarded limit [Thiyam et al., Phys. Rev. Lett. 120, 131601 (2018)], which is applied here to study the change in sign and magnitude of the torque with separation distance in biaxial black phosphorus having excess charge carriers. The study is carried out both in vacuum and in a background fluid medium. The presence of extra charge carriers and that of an intervening fluid medium are both found to promote enhancement of the magnitude of the torque between identical slabs. The degree of enhancement of the magnitude of torque increases not only with an increased carrier concentration but also with separation distance. In the nonidentical case when different planes of anisotropic black phosphorus face each other, owing to the nonmonotonic characteristic of the sign-reversal effect of the torque, the enhancement by carrier addition and intervening medium also becomes nonmonotonic with distance. In the presence of a background medium, the nonmonotonic degree of enhancement of the torque with distance is observed even between identical slabs.

  • 315.
    Tjernshaugen, Johanne Bratland
    et al.
    Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
    Amundsen, Morten
    Nordita SU.
    Linder, Jacob
    Center for Quantum Spintronics, Department of Physics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
    Superconducting phase diagram and spin diode effect via spin accumulation2024In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 109, no 9, article id 094516Article in journal (Refereed)
    Abstract [en]

    Spin-split superconductors offer new functionality compared to conventional superconductors such as diode effects and efficient thermoelectricity. The superconducting state can nevertheless only withstand a small amount of spin splitting. Here, we self-consistently determine the spin transport properties and the phase diagram of a spin-split superconductor in the presence of an injected spin accumulation. Energy and spin relaxation are accounted for in the relaxation time approximation via a single effective inelastic scattering parameter. We find that the spin-splitting field in the superconductor enables a spin diode effect. Moreover, we consider the superconducting phase diagram of a system in contact with a spin accumulation and in the presence of spin relaxation, and find that the inclusion of energy and spin relaxation alters the phase diagram qualitatively. In particular, these mechanisms turn out to induce a superconducting state in large parts of the phase diagram where a normal state would otherwise be the ground state. We identify an Fulde-Ferrel-Larkin-Ovchinnikkov-like state even in the presence of impurity scattering, which can be controllably turned on and off via the electrically induced spin accumulation. We explain the underlying physics from how the superconducting order parameter depends on the nonequilibrium modes in the system as well as the behavior of these modes in the presence of energy and spin relaxation when a spin-splitting field is present.

  • 316.
    Triola, Christopher
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Odd-frequency superconductivity in driven systems2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 9, article id 094518Article in journal (Refereed)
    Abstract [en]

    We show that Berezinskii's classification of the symmetries of Cooper pair amplitudes holds for driven systems even in the absence of translation invariance. We then consider a model Hamiltonian for a superconductor coupled to an external driving potential and, treating the drive as a perturbation, we investigate the corrections to the anomalous Green's function, density of states, and spectral function. We find that in the presence of an external drive the anomalous Green's function develops terms that are odd in frequency and that the same mechanism responsible for these odd-frequency terms generates additional features in the density of states and spectral function.

  • 317.
    Triola, Christopher
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Los Alamos National Laboratory, United States; ETH Institute for Theoretical Studies, Switzerland.
    Pair symmetry conversion in driven multiband superconductors2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 22, article id 224518Article in journal (Refereed)
    Abstract [en]

    It was recently shown that odd-frequency superconducting pair amplitudes can be induced in conventional superconductors subjected to a spatially nonuniform time-dependent drive. It has also been shown that, in the presence of interband scattering, multiband superconductors will possess bulk odd-frequency superconducting pair amplitudes. In this work we build on these previous results to demonstrate that by subjecting a multiband superconductor with interband scattering to a time-dependent drive, even-frequency pair amplitudes can be converted to odd-frequency pair amplitudes and vice versa. We will discuss the physical conditions under which these pair symmetry conversions can be achieved and possible experimental signatures of their presence.

  • 318.
    Triola, Christopher
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Pertsova, Anna
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Markiewicz, Robert S.
    Balatsky, Alexander V.
    Excitonic gap formation in pumped Dirac materials2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 20, article id 205410Article in journal (Refereed)
    Abstract [en]

    Recent pump-probe experiments demonstrate the possibility that Dirac materials may be driven into transient excited states describable by two chemical potentials, one for the electrons and one for the holes. Given the Dirac nature of the spectrum, such an inverted population allows the optical tunability of the density of states of the electrons and holes, effectively offering control of the strength of the Coulomb interaction. Here we discuss the feasibility of realizing transient excitonic instabilities in optically pumped Dirac materials. We demonstrate, theoretically, the reduction of the critical coupling leading to the formation of a transient condensate of electron-hole pairs and identify signatures of this state. Furthermore, we provide guidelines for experiments by both identifying the regimes in which such exotic many-body states are more likely to be observed and estimating the magnitude of the excitonic gap for a few important examples of existing Dirac materials. We find a set of material parameters for which our theory predicts large gaps and high critical temperatures and which could be realized in future Dirac materials. We also comment on transient excitonic instabilities in three-dimensional Dirac and Weyl semimetals. This study provides an example of a transient collective instability in driven Dirac materials.

  • 319. Tupitsyn, Igor S.
    et al.
    Mishchenko, Andrey S.
    Nagaosa, Naoto
    Prokof'ev, Nikolay
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. University of Massachusetts, United States.
    Coulomb and electron-phonon interactions in metals2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 15, article id 155145Article in journal (Refereed)
    Abstract [en]

    An accurate and consistent theory of phonons in metals requires that all long-range Coulomb interactions between charged particles (electrons and ions) be treated on equal footing. So far, all attempts to deal with this nonperturbative system were relying on uncontrolled approximations in the absence of small parameters. In this paper, we develop the diagrammatic Monte Carlo approach for a two-component Coulomb system that obtains the solution to this fundamental problem in an approximation-free way by computing vertex corrections from higher-order skeleton graphs. The feasibility of the method is demonstrated by calculating the spectrum of longitudinal acoustic phonons in a simple cubic lattice, determining their sound velocity, and obtaining the phonon spectral densities by analytic continuation of the Matsubara-Green's functions. Final results are checked against the lowest-order fully self-consistent GW approximation in both adiabatic and nonadiabatic regimes.

  • 320.
    Turrini, A. A.
    et al.
    Paul Scherrer Inst, Lab Neutron Scattering & Imaging, CH-5232 Villigen, Switzerland.;Dept Quantum Matter Phys, 24 Quai Ernest Ansennet, CH-1211 Geneva 4, Switzerland..
    Harman-Clarke, A.
    UCL, London Ctr Nanotechnol, 17-19 Gordon St, London W H 0AH, England.;UCL, Dept Phys & Astron, 17-19 Gordon St, London W H 0AH, England.;Univ Lyon, Lab Phys, CNRS, ENS Lyon, F-69342 Lyon, France..
    Haeseler, G.
    Univ Lyon, Lab Phys, CNRS, ENS Lyon, F-69342 Lyon, France..
    Fennell, T.
    Paul Scherrer Inst, Lab Neutron Scattering & Imaging, CH-5232 Villigen, Switzerland..
    Wood, I. G.
    UCL, Dept Earth Sci, London W E 6BT, England..
    Henelius, Patrik
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Bramwell, S. T.
    UCL, London Ctr Nanotechnol, 17-19 Gordon St, London W H 0AH, England.;UCL, Dept Phys & Astron, 17-19 Gordon St, London W H 0AH, England..
    Holdsworth, P. C. W.
    Univ Lyon, Lab Phys, CNRS, ENS Lyon, F-69342 Lyon, France..
    Tunable critical correlations in kagome ice2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 9, article id 094403Article in journal (Refereed)
    Abstract [en]

    We present a comprehensive experimental and theoretical study of the kagome ice Coulomb phase that explores the fine-tuning of critical correlations by applied field, temperature, and crystal orientation. The continuous modification of algebraic correlations is observed by polarized neutron scattering experiments and is found to be well described by numerical simulations of an idealized model. We further clarify the thermodynamics of field-tuned Kasteleyn transitions and demonstrate some dramatic finite-size-scaling properties that depend on how topological string defects wind around the system boundaries. We conclude that kagome ice is a remarkable example of a critical and topological state in a real system that may be subject to fine experimental control.

  • 321.
    Twengström, Mikael
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Bovo, L.
    UCL, London Ctr Nanotechnol, 17-19 Gordon St, London W H 0AH, England.;UCL, Dept Phys & Astron, 17-19 Gordon St, London W H 0AH, England.;UCL, Dept Innovat & Enterprise, 90 Tottenham Court Rd, London W1T 4TJ, England..
    Petrenko, O. A.
    Univ Warwick, Dept Phys, Coventry CV4 7AL, W Midlands, England..
    Bramwell, S. T.
    UCL, London Ctr Nanotechnol, 17-19 Gordon St, London W H 0AH, England.;UCL, Dept Phys & Astron, 17-19 Gordon St, London W H 0AH, England..
    Henelius, Patrik
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory. Abo Akad Univ, Fac Sci & Engn, Turku 20500, Finland..
    LiHoF4: Cuboidal demagnetizing factor in an Ising ferromagnet2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, no 14, article id 144426Article in journal (Refereed)
    Abstract [en]

    The demagnetizing factor can have an important effect on physical properties, yet its role in determining the behavior of nonellipsoidal samples remains to be fully explored. We present a detailed study of the role of spin symmetry in determining the demagnetizing factor of cuboids, focusing, as a model example, on the Ising dipolar ferromagnet LiHoF4. We distinguish two different functions: the demagnetizing factor as a function of intrinsic susceptibility N(chi) and the demagnetizing factor as a function of temperature N(T). For a given nonellipsoidal sample, the function N(chi) depends only on dipolar terms in the spin Hamiltonian, but apart from in the limits x -> 0 and x -> infinity, it is a different function for different spin symmetries. The function N(T) is less universal, depending on exchange terms and other details of the spin Hamiltonian. We apply a recent theory to calculate these functions for spherical and cuboidal samples of LiHoF4. The theoretical results are compared with N(chi) and N(T) derived from experimental measurements of the magnetic susceptibility of corresponding samples of LiHoF4, both above and below its ferromagnetic transition at T-c = 1.53 K. Close agreement between theory and experiment is demonstrated, showing that the intrinsic susceptibility of LiHoF4 and other strongly magnetic systems can be accurately estimated from measurements on cuboidal samples. Our results further show that for cuboids, and implicitly for any sample shape, N(chi) below the ordering transition takes the value N (infinity). This confirms and extends the scope of earlier observations that the intrinsic susceptibility of ferromagnets remains divergent below the transition, in contradiction to the implications of broken symmetry. We discuss the topological and microscopic origins of this result.

  • 322.
    Tyner, Alexander C.
    et al.
    Nordita SU, Graduate Program in Applied Physics, Northwestern University, Evanston, Illinois 60208, USA.
    Sur, Shouvik
    Department of Physics and Astronomy, Rice Center for Quantum Materials, Rice University, Houston, Texas 77005, USA.
    Dipolar Weyl semimetals2024In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 109, no 8, p. 292-302, article id L081101Article in journal (Refereed)
    Abstract [en]

    In Weyl semimetals, Weyl points act as monopoles and antimonopoles of the Berry curvature, with a monopole-antimonopole pair producing a net-zero Berry flux. When inversion symmetry is preserved, the two-dimensional (2D) planes that separate a monopole-antimonopole pair of Weyl points carry quantized Berry flux. In this work, we introduce a class of symmetry-protected Weyl semimetals which host monopole-antimonopole pairs of Weyl points that generate a dipolar Berry flux. Thus, both monopolar and dipolar Berry fluxes coexist in the Brillouin zone, which results in two distinct types of topologically nontrivial planes separating the Weyl points, carrying either a quantized monopolar or a quantized dipolar flux. We construct a topological invariant - the staggered Chern number - to measure the latter, and employ it to topologically distinguish between various Weyl points. Finally, through a minimal two-band model, we investigate physical signatures of bulk topology, including surface Fermi arcs, zero-energy hinge states, and response to insertion of a π-flux vortex.

  • 323.
    Tyner, Alexander C.
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Graduate Program in Applied Physics, Northwestern University, Evanston, Illinois 60208, USA; Nordita, Stockholm University 106 91 Stockholm, Sweden.
    Sur, Shouvik
    Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208, USA; Department of Physics and Astronomy, Rice Center for Quantum Materials, Rice University, Houston, TX 77005, USA.
    Zhou, Qunfei
    Materials Research Science and Engineering Center, Northwestern University, Evanston, Illinois 60208, USA; Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, USA; Department of Physics and Astronomy, University of Kansas, Lawrence, KS, USA.
    Puggioni, Danilo
    Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA.
    Darancet, Pierre
    Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois 60439, USA; Northwestern Argonne Institute for Science and Engineering, Evanston, Illinois 60208, USA.
    Rondinelli, James M.
    Graduate Program in Applied Physics, Northwestern University, Evanston, Illinois 60208, USA; Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208, USA; Northwestern Argonne Institute for Science and Engineering, Evanston, Illinois 60208, USA.
    Goswami, Pallab
    Graduate Program in Applied Physics, Northwestern University, Evanston, Illinois 60208, USA; Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208, USA.
    In-plane Wilson loop for measurement of quantized non-Abelian Berry flux2024In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 109, no 19, article id 195149Article in journal (Refereed)
    Abstract [en]

    Band topology of anomalous quantum Hall insulators can be precisely addressed by computing the Chern numbers of constituent nondegenerate bands, describing the presence of quantized, Abelian Berry flux through the two-dimensional Brillouin zone. Can Berry flux be captured for the SU(2) Berry connection of two-fold degenerate bands in spinful materials preserving space-inversion (P) and time-reversal (T) symmetries without detailed knowledge of underlying basis We address this question by investigating the correspondence between a non-Abelian generalization of Stokes' theorem and the manifestly gauge-invariant eigenvalues of Wilson loops computed along in-plane contours which preserve the underlying crystalline symmetry. The importance of this correspondence is elucidated by performing natural number resolved classification of ab initio band structures of three-dimensional, Dirac materials. Our work underscores how identification of quantized Berry flux, both Abelian and non-Abelian, offers a unified framework for addressing first-order and higher-order topology of insulators and semimetals.

  • 324.
    Ukleev, V
    et al.
    Paul Scherrer Inst, Lab Neutron Scattering & Imaging LNS, CH-5232 Villigen, Switzerland..
    Tarnavich, V
    Natl Res Ctr, Kurchatov Inst, Petersburg Nucl Phys Inst, Gatchina 188300, Russia..
    Tartakovskaya, E.
    Natl Acad Sci Ukraine, Inst Magnetism, UA-03142 Kiev, Ukraine.;Kiev Natl Univ, Inst High Technol, UA-03022 Kiev, Ukraine..
    Lott, D.
    Helmholtz Zentrum Geesthacht, Inst Mat Res, Max Planck Str 1, D-21502 Geesthacht, Germany..
    Kapaklis, V
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Oleshkevych, Anna
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science. Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Gargiani, P.
    ALBA Synchrotron Light Source, CELLS Expt Div, E-08290 Barcelona, Spain..
    Valvidares, M.
    ALBA Synchrotron Light Source, CELLS Expt Div, E-08290 Barcelona, Spain..
    White, J. S.
    Paul Scherrer Inst, Lab Neutron Scattering & Imaging LNS, CH-5232 Villigen, Switzerland..
    Grigoriev, S. , V
    Coherent charge and magnetic ordering in Ho/Y superlattice revealed by element-selective x-ray scattering2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 13, article id 134417Article in journal (Refereed)
    Abstract [en]

    Magnetic rare-earth/nonmagnetic metal superlattices are well-known to display chiral spin helices in the rare-earth layers that propagate coherently across the nonmagnetic layers. However, the underlying mechanism that preserves the magnetic phase and chirality coherence across the nonmagnetic layers has remained elusive. In this paper, we use resonant and element-specific x-ray scattering to evidence directly the formation of two fundamentally different long-range modulations in a holmium/yttrium (Ho/Y) multilayer: the known Ho chiral spin helix with periodicity 25 angstrom and a newly observed charge density wave with periodicity 16 angstrom that propagates through both the Ho and nonmagnetic Y layer. With x-ray circular magnetic dichroism measurements ruling out the existence of a magnetic proximity effect induced moment in the nonmagnetic Y layers, we propose that the charge density wave is also chiral, thus providing the means for the transmittance of magnetic chirality coherence between Ho layers.

  • 325.
    Umegaki, Izumi
    et al.
    High Energy Accelerator Res Org KEK, Inst Mat Struct Sci, Tokai, Ibaraki 3191106, Japan.;J PARC Ctr, Mat & Life Sci Expt Facil MLF Div, Tokai, Ibaraki 3191195, Japan.;Grad Univ Adv Studies SOKENDAI, Dept Mat Struct Sci, Tsukuba, Ibaraki 3050801, Japan..
    Moriyama, Kodai
    Kyoto Univ, Grad Sch Sci, Dept Chem, Kyoto 6068502, Japan.;Univ Tokyo, Inst Solid State Phys, Kashiwa, Chiba 2778581, Japan..
    Yoshinaga, Kohei
    Kyoto Univ, Grad Sch Sci, Dept Chem, Kyoto 6068502, Japan..
    Ohishi, Kazuki
    Comprehens Res Org Sci & Soc CROSS, Neutron Sci & Technol Ctr, Tokai, Ibaraki 3191106, Japan..
    Elson, Frank
    KTH, School of Engineering Sciences (SCI), Applied Physics, Light and Matter Physics.
    Miniotaite, Ugne
    KTH, School of Engineering Sciences (SCI), Applied Physics, Light and Matter Physics.
    Palm, Rasmus
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Light and Matter Physics.
    Forslund, Ola Kenji
    Univ Zurich, Phys Inst, Winterthurerstr 190, CH-8057 Zurich, Switzerland.;Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Sassa, Yasmine
    KTH, School of Engineering Sciences (SCI), Applied Physics, Light and Matter Physics.
    Sugiyama, Soh
    Nagoya Univ, Dept Phys, Nagoya, Aichi 4648602, Japan..
    Morris, Gerald D.
    TRIUMF, Ctr Mol & Mat Sci, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada..
    Hitti, Bassam
    TRIUMF, Ctr Mol & Mat Sci, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada..
    Michioka, Chishiro
    Kyoto Univ, Grad Sch Sci, Dept Chem, Kyoto 6068502, Japan..
    Ueda, Hiroaki
    Shimane Univ, Inst Adv Mat Res & Dev, Matsue, Shimane 6908504, Japan..
    Yoshimura, Kazuyoshi
    Kyoto Univ, Grad Sch Engn, Dept Energy & Hydrocarbon Chem, Kyoto 6158510, Japan..
    Sugiyama, Jun
    Comprehens Res Org Sci & Soc CROSS, Neutron Sci & Technol Ctr, Tokai, Ibaraki 3191106, Japan.;Japan Atom Energy Agcy, Adv Sci Res Ctr, Tokai, Ibaraki 3191195, Japan..
    Magnetic phase diagram of Eu 1- x Ca x Co 2 P 2 determined using muon spin rotation and relaxation2024In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 109, no 14, article id 144408Article in journal (Refereed)
    Abstract [en]

    The present study investigated the magnetic nature of a solid solution system consisting of EuCo2P2 and CaCo2P2 using a muon spin rotation and relaxation (mu +SR) technique, which is sensitive to local magnetic environments. The former compound EuCo2P2 is known to enter an incommensurate helical antiferromagnetic (AF) phase below 66 K with neutrons, which was confirmed by the present mu +SR. The magnitude of the ordered Eu moments proposed with neutrons was found to be consistent with that estimated by mu +SR. Furthermore, the latter lattice-collapsed tetragonal phase compound CaCo2P2 is known to enter an A-type AF phase below 90 K, and mu +SR measurements on single crystals revealed the presence of a spin reorientation transition at around 40 K, below which the A-type AF order is likely to be completed. Although all Eu1-xCaxCo2P2 compounds were found to enter a magnetic phase at low temperatures regardless of x, a static ordered state was formed only at the vicinity of the two end compounds, i.e., 0 x 0.4 and 0.9 x 1. Instead, a disordered state, i.e., a random spin-glass state, short-range ordered state, or highly fluctuating state was found in the x range between 0.4 and 0.9, even at the lowest measured temperature (2 K). Together with the magnetization data, our findings clarified the magnetic phase diagram of Eu1-xCaxCo2P2, where a ferromagnetic exchange interaction between Co ions through the Eu2+ ion competes with a direct AF interaction among the Co ions, particularly in the x range between 0.57 and 0.9. This competition yielded multiple phases in Eu1-xCaxCo2P2.

  • 326. Van Houcke, Kris
    et al.
    Tupitsyn, Igor S.
    Mishchenko, Andrey S.
    Prokof'ev, Nikolay V.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics. Kurchatov Institute, Russia.
    Dielectric function and thermodynamic properties of jellium in the GW approximation2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 19, article id 195131Article in journal (Refereed)
    Abstract [en]

    The fully self-consistent GW approximation is an established method for electronic structure calculations. Its most serious deficiency is known to be an incorrect prediction of the dielectric response. In this work, we examine the GW approximation for the homogeneous electron gas and find that problems with the dielectric response are drastically improved by enforcing the particle-number conservation law in the polarization function. We also find that previously reported data for the ground-state energy contradict each other well outside of reported error bounds. Some of these results created a false impression of how accurate the fully self-consistent GW approximation is. Our two independent implementations of the GW method agree with the data plotted in X.-Z. Yan [Phys. Rev. E 84, 016706 (2011)], thus confirming only that data set. We also present values for other key Fermi-liquid properties.

  • 327.
    Vargunin, Artjom
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Silaev, M. A.
    Self-consistent calculation of the flux-flow conductivity in diffusive superconductors2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 21, article id 214507Article in journal (Refereed)
    Abstract [en]

    In the framework of Keldysh-Usadel kinetic theory, we study the temperature dependence of flux-flow conductivity (FFC) in diffusive superconductors. By using self-consistent vortex solutions we find the exact values of dimensionless parameters that determine the diffusion-controlled FFC both in the limit of the low temperatures and close to the critical one. Taking into account the electron-phonon scattering, we study the transition between flux-flow regimes controlled by either the diffusion or the inelastic relaxation of nonequilibrium quasiparticles. We demonstrate that the inelastic electron-phonon relaxation leads to the strong suppression of FFC compared to the previous estimates, making it possible to obtain numerical agreement with experimental results.

  • 328.
    Vasiloiu, Loredana M.
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Tiwari, Apoorv
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Bardarson, Jens H.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Dephasing-enhanced Majorana zero modes in two-dimensional and three-dimensional higher-order topological superconductors2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, no 6, article id L060307Article in journal (Refereed)
    Abstract [en]

    The one-dimensional (1D) Kitaev model in the topological phase, with open boundary conditions, hosts Majorana zero modes. These are fermion parity-odd operators that almost commute with the Hamiltonian and manifest in long coherence times for edge degrees of freedom. We obtain higher-dimensional counterparts of such Majorana operators by explicitly computing their closed form expressions in models describing 2D and 3D higher-order superconductors. Due to the existence of such Majorana zero modes, the coherence time of the infinite temperature autocorrelation function of the corner Majorana operators in these models diverges with the linear system size. In the presence of a certain class of orbital-selective dissipative dynamics, the coherence times of half of the corner Majorana operators are enhanced, while the time correlations corresponding to the remaining corner Majoranas decay much faster as compared with the unitary case. We numerically demonstrate robustness of the coherence times to the presence of disorder.

  • 329.
    Vergara, I
    et al.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Magnaterra, M.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Warzanowski, P.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Attig, J.
    Univ Cologne, Inst Theoret Phys, D-50937 Cologne, Germany..
    Kunkemöller, S.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Khomskii, D. , I
    Braden, M.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Hermanns, Maria
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, AlbaNova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden.;Stockholm Univ, SE-10691 Stockholm, Sweden..
    Grüninger, M.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Spin-orbit coupling and crystal-field splitting in Ti-doped Ca2RuO4 studied by ellipsometry2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, no 8, article id 085103Article in journal (Refereed)
    Abstract [en]

    In Ca2RuO4, the competition of spin-orbit coupling ζ and tetragonal crystal-field splitting ΔCF has been discussed controversially for many years. The orbital occupation depends on ΔCF/ζ, which allows us to address this ratio via the optical spectral weights of the lowest intersite Mott-Hubbard excitations. We study the optical conductivity of Ca2Ru0.99Ti0.01O4 in the range of 0.75–5 eV by ellipsometry, using the large single crystals that can be grown for small Ti concentrations. Based on a local multiplet calculation, our analysis results in 2.4≤ΔCF/ζ≲4 at 15 K. The dominant crystal field yields a ground state close to xy orbital order but spin-orbit coupling is essential for a quantitative description of the properties. Furthermore, we observe a pronounced decrease of ΔCF with increasing temperature, as expected based on the reduction of octahedral distortions.

  • 330.
    Versteegh, Marijn A. M.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Steinhauer, Stephan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Bajo, Josip
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Lettner, Thomas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Soro, Ariadna
    KTH, School of Engineering Sciences (SCI), Applied Physics. Chalmers Univ Technol, Dept Microtechnol & Nanosci, Gothenburg, Sweden..
    Romanova, Alena
    KTH, School of Engineering Sciences (SCI), Applied Physics. Johannes Gutenberg Univ Mainz, Inst Phys, D-55099 Mainz, Germany..
    Gyger, Samuel
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Schweickert, Lucas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Mysyrowicz, Andre
    Ecole Polytech, CNRS, Lab Opt Appl, ENSTA, F-91762 Palaiseau, France..
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Giant Rydberg excitons in Cu2O probed by photoluminescence excitation spectroscopy2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 24, article id 245206Article in journal (Refereed)
    Abstract [en]

    Rydberg excitons are, with their ultrastrong mutual interactions, giant optical nonlinearities, and very high sensitivity to external fields, promising for applications in quantum sensing and nonlinear optics at the singlephoton level. To design quantum applications it is necessary to know how Rydberg excitons and other excited states relax to lower-lying exciton states. Here, we present photoluminescence excitation spectroscopy as a method to probe transition probabilities from various excitonic states in cuprous oxide. We show giant Rydberg excitons at T = 38 mK with principal quantum numbers up to n = 30, corresponding to a calculated diameter of 3 mu m.

  • 331.
    Volckaert, Klara
    et al.
    Aarhus Univ, Interdisciplinary Nanosci Ctr, Dept Phys & Astron, DK-8000 Aarhus C, Denmark..
    Rostami, Habib
    Nordita SU.
    Biswas, Deepnarayan
    Univ StAndrews, Sch Phys & Astron, SUPA, St Andrews KY16 9SS, Fife, Scotland..
    Markovic, Igor
    Univ StAndrews, Sch Phys & Astron, SUPA, St Andrews KY16 9SS, Fife, Scotland.;Max Planck Inst Chem Phys Solids, Nothnitzer Str 40, D-01187 Dresden, Germany..
    Andreatta, Federico
    Aarhus Univ, Interdisciplinary Nanosci Ctr, Dept Phys & Astron, DK-8000 Aarhus C, Denmark..
    Sanders, Charlotte E.
    STFC Rutherford Appleton Lab, Cent Laser Facil, Harwell 0X11 0QX, Berks, England..
    Majchrzak, Paulina
    STFC Rutherford Appleton Lab, Cent Laser Facil, Harwell 0X11 0QX, Berks, England..
    Cacho, Cephise
    STFC Rutherford Appleton Lab, Cent Laser Facil, Harwell 0X11 0QX, Berks, England..
    Chapman, Richard T.
    STFC Rutherford Appleton Lab, Cent Laser Facil, Harwell 0X11 0QX, Berks, England..
    Wyatt, Adam
    STFC Rutherford Appleton Lab, Cent Laser Facil, Harwell 0X11 0QX, Berks, England..
    Springate, Emma
    STFC Rutherford Appleton Lab, Cent Laser Facil, Harwell 0X11 0QX, Berks, England..
    Lizzit, Daniel
    Elettra Sincrotrone Trieste, SS 14 Km 163-5, I-34149 Trieste, Italy..
    Bignardi, Luca
    Elettra Sincrotrone Trieste, SS 14 Km 163-5, I-34149 Trieste, Italy.;Univ Trieste, Dept Phys, Via Valerio 2, I-34127 Trieste, Italy..
    Lizzit, Silvano
    Elettra Sincrotrone Trieste, SS 14 Km 163-5, I-34149 Trieste, Italy..
    Mahatha, Sanjoy K.
    Aarhus Univ, Interdisciplinary Nanosci Ctr, Dept Phys & Astron, DK-8000 Aarhus C, Denmark..
    Bianchi, Marco
    Aarhus Univ, Interdisciplinary Nanosci Ctr, Dept Phys & Astron, DK-8000 Aarhus C, Denmark..
    Lanata, Nicola
    Aarhus Univ, Interdisciplinary Nanosci Ctr, Dept Phys & Astron, DK-8000 Aarhus C, Denmark..
    King, Phil D. C.
    Univ StAndrews, Sch Phys & Astron, SUPA, St Andrews KY16 9SS, Fife, Scotland..
    Miwa, Jill A.
    Aarhus Univ, Interdisciplinary Nanosci Ctr, Dept Phys & Astron, DK-8000 Aarhus C, Denmark..
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Hofmann, Philip
    Aarhus Univ, Interdisciplinary Nanosci Ctr, Dept Phys & Astron, DK-8000 Aarhus C, Denmark..
    Ulstrup, Soren
    Aarhus Univ, Interdisciplinary Nanosci Ctr, Dept Phys & Astron, DK-8000 Aarhus C, Denmark..
    Momentum-resolved linear dichroism in bilayer MoS22019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 24, article id 241406Article in journal (Refereed)
    Abstract [en]

    In solid state photoemission experiments it is possible to extract information about the symmetry and orbital character of the electronic wave functions via the photoemission selection rules that shape the measured intensity. This approach can be expanded in a pump-probe experiment where the intensity contains additional information about interband excitations induced by an ultrafast laser pulse with tunable polarization. Here, we find an unexpected strong linear dichroism effect (up to 42.4%) in the conduction band of bilayer MoS2, when measuring energy- and momentum-resolved snapshots of excited electrons by time- and angle-resolved photoemission spectroscopy. We model the polarization-dependent photoemission intensity in the transiently populated conduction band using the semiconductor Bloch equations. Our theoretical analysis reveals a strongly anisotropic momentum dependence of the optical excitations due to intralayer single-particle hopping, which explains the observed linear dichroism.

  • 332.
    von Malottki, Stephan
    et al.
    Univ Kiel, Inst Theoret Phys & Astrophys, Leibnizstr 15, D-24098 Kiel, Germany..
    Bessarab, Pavel F.
    Univ Kiel, Inst Theoret Phys & Astrophys, Leibnizstr 15, D-24098 Kiel, Germany.;ITMO Univ, St Petersburg 197101, Russia..
    Haldar, Soumyajyoti
    Univ Kiel, Inst Theoret Phys & Astrophys, Leibnizstr 15, D-24098 Kiel, Germany..
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala Univ, Dept Phys & Astron, Uppsala, Sweden.
    Heinze, Stefan
    Univ Kiel, Inst Theoret Phys & Astrophys, Leibnizstr 15, D-24098 Kiel, Germany..
    Skyrmion lifetime in ultrathin films2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 6, article id 060409Article in journal (Refereed)
    Abstract [en]

    We show that thermal stability of skyrmions due to entropic effects can be strongly affected by external control parameters such as magnetic field and interface composition. The lifetimes of isolated skyrmions in atomic Pd/Fe bilayers on Ir(111) and on Rh(111) are calculated in the framework of harmonic transition state theory based on an atomistic spin model parametrized from density functional theory. Depending on the system the attempt frequency for skyrmion collapse can change by up to nine orders of magnitude with the strength of the applied magnetic field. We demonstrate that this effect is due to a drastic change of entropy with skyrmion radius which opens a route toward stabilizing sub-10-nm skyrmions at room temperature.

  • 333.
    Wagner, Glenn
    et al.
    Rudolf Peierls Ctr Theoret Phys, Oxford OX1 3PU, England.;Univ Calif Santa Barbara, Kavli Inst Theoret Phys, Santa Barbara, CA 93106 USA..
    Røising, Henrik S.
    Rudolf Peierls Ctr Theoret Phys, Oxford OX1 3PU, England.; Stockholm Univ, Hannes Alfvens Vag 12, SE-10691 Stockholm, Sweden.;Nordita SU.
    Flicker, Felix
    Rudolf Peierls Ctr Theoret Phys, Oxford OX1 3PU, England.;Cardiff Univ, Sch Phys & Astron, Cardiff CF24 3AA, Wales.;Univ Bristol, Sch Math, Bristol BS8 1TW, Avon, England..
    Simon, Steven H.
    Rudolf Peierls Ctr Theoret Phys, Oxford OX1 3PU, England..
    Microscopic Ginzburg-Landau theory and singlet ordering in Sr2RuO42021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 13, article id 134506Article in journal (Refereed)
    Abstract [en]

    The long-standing quest to determine the superconducting order of Sr2RuO4 (SRO) has received renewed attention after recent nuclear magnetic resonance (NMR) Knight shift experiments have cast doubt on the possibility of spin-triplet pairing in the superconducting state. As a putative solution, encompassing a body of experiments conducted over the years, a (d + ig)-wave order parameter caused by an accidental near degeneracy has been suggested [S. A. Kivelson et al., npj Quantum Mater. 5, 43 (2020)]. Here we develop a general Ginzburg-Landau theory for multiband superconductors. We apply the theory to SRO and predict the relative size of the order parameter components. The heat capacity jump expected at the onset of the second-order parameter component is found to be above the current threshold deduced by the experimental absence of a second jump. Our results tightly restrict theories of d + ig order, and other candidates caused by a near degeneracy, in SRO. We discuss possible solutions to the problem.

  • 334.
    Wang, Wenlong
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory. Sichuan Univ, Coll Phys, Chengdu 610065, Peoples R China..
    Diaz-Mendez, Rogelio
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Wallin, Mats
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Lidmar, Jack
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Physics, Statistical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Pinning effects in a two-dimensional cluster glass2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 14, article id 144206Article in journal (Refereed)
    Abstract [en]

    We study numerically the nonequilibrium glass formation and depinning transition of a system of two-dimensional cluster-forming monodisperse particles in the presence of pinning disorder. The pairwise interaction potential is nonmonotonic and is motivated by the intervortex forces in type-1.5 superconductors but also applies to a variety of other systems. Such systems can form cluster glasses due to the intervortex interactions following a thermal quench, without underlying disorder. We study the effects of vortex pinning in these systems. We find that a small density of pinning centers of moderate depth has a limited effect on vortex glass formation, i.e., formation of vortex glasses is dominated by intervortex interactions. At higher densities, pinning can significantly affect glass formation. The cluster glass depinning, under a constant driving force, is found to be plastic, with features distinct from non-cluster-forming systems such as clusters merging and breaking. We find that, in general, vortices with cluster-forming interaction forces can exhibit stronger pinning effects than regular vortices.

  • 335.
    Wang, Wenlong
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Meier, Hannes
    KTH, School of Engineering Sciences (SCI), Physics, Statistical Physics.
    Lidmar, Jack
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Wallin, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Three-dimensional universality class of the Ising model with power-law correlated critical disorder2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 14, article id 144204Article in journal (Refereed)
    Abstract [en]

    We use large-scale Monte Carlo simulations to test the Weinrib-Halperin criterion that predicts new universality classes in the presence of sufficiently slowly decaying power-law correlated quenched disorder. While new universality classes are reasonably well established, the predicted exponents are controversial. We propose a method of growing such correlated disorder using the three-dimensional Ising model as a benchmark system for both generating disorder and studying the resulting phase transition. Critical equilibrium configurations of a disorder-free system are used to define the two-value distributed random bonds with a small power-law exponent given by the pure Ising exponent. Finite-size scaling analysis shows a new universality class with a single phase transition, but the critical exponents nu(d) = 1.13(5), eta(d) = 0.48(3) differ significantly from theoretical predictions. We find that depending on the details of the disorder generation, disorder-averaged quantities can develop peaks at two temperatures for finite sizes. Finally, a layer model with the two values of bonds spatially separated in halves of the system genuinely has multiple phase transitions, and thermodynamic properties can be flexibly tuned by adjusting the model parameters.

  • 336.
    Weston, Daniel
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Physics, Statistical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Composite order in SU(N) theories coupled to an Abelian gauge field2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 7, article id 075116Article in journal (Refereed)
    Abstract [en]

    We consider SU(N)-symmetric Ginzburg-Landau models coupled to a noncompact Abelian gauge field focusing on the case N > 2 at finite temperature. We show that, at least for sufficiently large gauge-field coupling constants, these models have two phase transitions. The intermediate phase between the symmetric and low-temperature phases is a state with composite neutral order and no Meissner effect. In this neutral phase the system spontaneously breaks only the symmetry associated with phase differences and density differences between components. For N > 2, in contrast to the SU(2) case, the neutral state cannot be mapped onto an O(M) model. We term this state the SU(N)(n) phase.

  • 337.
    Willman, Jonathan T.
    et al.
    Univ S Florida, Dept Phys, Tampa, FL 33620 USA..
    Nguyen-Cong, Kien
    Univ S Florida, Dept Phys, Tampa, FL 33620 USA..
    Williams, Ashley S.
    Univ S Florida, Dept Phys, Tampa, FL 33620 USA..
    Belonoshko, Anatoly
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Moore, Stan G.
    Sandia Natl Labs, Albuquerque, NM 87185 USA..
    Thompson, Aidan P.
    Sandia Natl Labs, Albuquerque, NM 87185 USA..
    Wood, Mitchell A.
    Sandia Natl Labs, Albuquerque, NM 87185 USA..
    Oleynik, Ivan I.
    Univ S Florida, Dept Phys, Tampa, FL 33620 USA..
    Machine learning interatomic potential for simulations of carbon at extreme conditions2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, no 18, article id L180101Article in journal (Refereed)
    Abstract [en]

    A spectral neighbor analysis (SNAP) machine learning interatomic potential (MLIP) has been developed for simulations of carbon at extreme pressures (up to 5 TPa) and temperatures (up to 20 000 K). This was achieved using a large database of experimentally relevant quantum molecular dynamics (QMD) data, training the SNAP potential using a robust machine learning methodology, and performing extensive validation against QMD and experimental data. The resultant carbon MLIP demonstrates unprecedented accuracy and transferability in predicting the carbon phase diagram, melting curves of crystalline phases, and the shock Hugoniot, all within 3% of QMD. By achieving quantum accuracy and efficient implementation on leadership-class high-performance computing systems, SNAP advances frontiers of classical MD simulations by enabling atomic-scale insights at experimental time and length scales.

  • 338.
    Winyard, Thomas
    et al.
    KTH, School of Engineering Sciences (SCI), Physics. University of Leeds, Leeds, LS2 9JT, United Kingdom.
    Silaev, Mihail
    Univ Jyvaskyla, Dept Phys, POB 35 YFL, FI-40014 Jyvaskyla, Finland.;Univ Jyvaskyla, Nanosci Ctr, POB 35 YFL, FI-40014 Jyvaskyla, Finland..
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Physics, Statistical Physics.
    Hierarchies of length-scale based typology in anisotropic U(1) s-wave multiband superconductors2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 6, article id 064509Article in journal (Refereed)
    Abstract [en]

    Since Ginzburg and Landau's seminal work in 1950, superconducting states have been classified by the hierarchy of the fundamental length scales of the theory, the magnetic-field penetration lengths and coherence lengths. In the simplest single-component case they form a dimensionless ratio kappa. The model was generalized by Ginzburg for anisotropic materials in 1952. In this paper we expand the above length-scale analysis to anisotropic multicomponent superconductors that can have multiple coherence lengths as well as multiple magnetic-field penetration lengths, leading to unconventional length-scale hierarchies. We demonstrate that the anisotropies in multiband superconductors lead to new regimes with various mixed hierarchies in different directions. For example, a regime is possible, where for a field applied in a certain direction coherence lengths are smaller than the magnetic-field penetration lengths in one of the perpendicular directions, whereas the penetration lengths are larger in the other direction. Focusing on a model of a clean anisotropic multiband s-wave supercocoductors we show exampes of a new regime where vortex cores overlap in one direction, resulting in attractive core-core interaction, while in the orthogonal direction the magnetic-field penetration length exceeds the coherence lengths, leading to dominance of repulsive current-current interaction, resulting in an unconventional magnetic response.

  • 339.
    Winyard, Thomas
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Silaev, Mihail
    Univ Jyvaskyla, Dept Phys, POB 35 YFL, FI-40014 Jyvaskyla, Finland.;Univ Jyvaskyla, Nanosci Ctr, POB 35 YFL, FI-40014 Jyvaskyla, Finland..
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Physics, Statistical Physics.
    Skyrmion formation due to unconventional magnetic modes in anisotropic multiband superconductors2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 2, article id 024501Article in journal (Refereed)
    Abstract [en]

    Multiband superconductors have a sufficient number of degrees of freedom to allow topological excitations characterized by skyrmionic topological invariants. In the most common, clean s-wave multiband systems, the interband Josephson and magnetic couplings favor composite vortex solutions, without a skyrmionic topological charge. It was discussed recently that certain kinds of anisotropies lead to hybridization of the interband phase difference (Leggett) mode with magnetic modes, dramatically changing the hydromagnetostatics of the system. Here we report this effect for a range of parameters that substantially alter the nature of the topological excitations, leading to solutions characterized by a nontrivial skyrmionic topological charge. The solutions have a form of a coreless texture formed of spatially separated but bound excitations in each band, namely fractional vortices, each carrying a fraction of the flux quantum. We demonstrate that in this regime there is a rich spectrum of skyrmion solutions, with various topological charges, that are robust with respect to changes of parameters of the system and present for a wide range of anisotropies.

  • 340.
    Woerle, Judith
    et al.
    Swiss Fed Inst Technol, Adv Power Semicond Lab, CH-8092 Zurich, Switzerland.;Paul Scherrrer Inst, Lab Micro & Nanotechnol, CH-5232 Villigen, Switzerland..
    Prokscha, Thomas
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Hallén, Anders
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electronics and Embedded systems.
    Grossner, Ulrike
    Swiss Fed Inst Technol, Adv Power Semicond Lab, CH-8092 Zurich, Switzerland..
    Interaction of low-energy muons with defect profiles in proton-irradiated Si and 4H-SiC2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 11, article id 115202Article in journal (Refereed)
    Abstract [en]

    Muon spin rotation (mu SR) with low-energy muons is a powerful nuclear method where electrical and magnetic properties of thin films can be investigated in a depth-resolved manner. Here, we present a study on proton-irradiated Si and 4H-SiC where the formation of the hydrogen-like muonium (Mu) is analyzed as a function of the proton dose. While the Mu formation is strongly suppressed in the highly defective region of the shallow proton stopping profile, the Mu signal quickly recovers for higher muon energies where the muons reach the untreated semiconductor bulk. A lower sensitivity limit of low-energy mu SR to crystal defects of around 10(17) to 10(18) cm(-3) is estimated. Our results demonstrate the high potential of this technique to nondestructively probe near-surface regions without the need for electronic device fabrication and to provide valuable complementary information when investigating defects in semiconductors.

  • 341. Wolter, A. U. B.
    et al.
    Corredor, L. T.
    Janssen, L.
    Nenkov, K.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Do, S. -H
    Choi, K. -Y
    Albrecht, R.
    Hunger, J.
    Doert, T.
    Vojta, M.
    Buechner, B.
    Field-induced quantum criticality in the Kitaev system alpha-RuCl32017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 4, article id 041405Article in journal (Refereed)
    Abstract [en]

    alpha-magnetic excitations akin to Kitaev's honeycomb-lattice spin liquid. We have performed a detailed specific-heat investigation at temperatures down to 0.4 K in applied magnetic fields up to 9 T for fields parallel to the ab plane. We find a suppression of the zero-field antiferromagnetic order, together with an increase of the low-temperature specific heat, with increasing field up to mu H-0(c) approximate to 6.9 T. Above H-c, the magnetic contribution to the low-temperature specific heat is strongly suppressed, implying the opening of a spin-excitation gap. Our data point toward a field-induced quantum critical point at H-c; this is supported by universal scaling behavior near H-c. Remarkably, the data also reveal the existence of a small characteristic energy scale well below 1 meV, above which the excitation spectrum changes qualitatively. We relate the data to theoretical calculations based on a J(1)-K-1-Gamma(1)-J(3) honeycomb model.

  • 342.
    Wong, Patrick J.
    et al.
    Nordita SU; Department of Physics, University of Connecticut, Storrs, Connecticut 06269, USA.
    Balatsky, Alexander V.
    Nordita SU; Department of Physics, University of Connecticut, Storrs, Connecticut 06269, USA.
    Appearance of odd-frequency superconductivity in a relativistic scenario2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, no 1, article id 014510Article in journal (Refereed)
    Abstract [en]

    Odd-frequency superconductivity is an exotic superconducting state in which the symmetry of the gap function is odd in frequency. Here, we show that an inherent odd-frequency mode emerges dynamically under application of a Lorentz transformation of the anomalous Green function with the general frequency-dependent gap function. To see this, we consider a Dirac model with quartic potential and perform a mean-field analysis to obtain a relativistic Bogoliubov-de Gennes system. Solving the resulting Gor'kov equations yields expressions for relativistic normal and anomalous Green functions. The form of the relativistically invariant pairing term is chosen such that it reduces to BCS form in the nonrelativistic limit. We choose an ansatz for the gap function in a particular frame which is even frequency and analyze the effects on the anomalous Green function under a boost into a relativistic frame. The odd-frequency pairing emerges dynamically as a result of the boost. In the boosted frame, the order parameter contains terms which are both even and odd in frequency. The relativistic correction to the anomalous Green function to first order in the boost parameter is completely odd in frequency. In this paper, we provide evidence that odd-frequency pairing may form intrinsically within relativistic superconductors.

  • 343. Xiao, D.
    et al.
    Tiberkevich, V.
    Liu, Y. H.
    Liu, Y. W.
    Mohseni, S. M.
    Chung, Sunjae
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF. University of Gothenburg, Sweden.
    Ahlberg, M.
    Slavin, A. N.
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF. University of Gothenburg, Sweden.
    Zhou, Yan
    Parametric autoexcitation of magnetic droplet soliton perimeter modes2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 2, article id 024106Article in journal (Refereed)
    Abstract [en]

    Recent experiments performed in current-driven nanocontacts with strong perpendicular anisotropy have shown that spin-transfer torque can drive self-localized spin waves [W. H. Rippard, A. M. Deac, M. R. Pufall, J. M. Shaw, M. W. Keller, S. E. Russek, G. E. W. Bauer, and C. Serpico, Phys. Rev. B 81, 014426 (2010); S. M. Mohseni, S. R. Sani, J. Persson, T. N. A. Nguyen, S. Chung, Y. Pogoryelov, and J. Akerman, Phys. Status Solidi RRL, 5, 432 (2011)], that above a certain intensity threshold can condense into a nanosized and highly nonlinear dynamic state known as a magnetic droplet soliton [S. M. Mohseni, S. R. Sani, J. Persson, T. N. A. Nguyen, S. Chung, Y. Pogoryelov, P. K. Muduli, E. Iacocca, A. Eklund, R. K. Dumas, S. Bonetti, A. Deac, M. A. Hoefer, and J. Akerman, Science 339, 1295 (2013)]. Here we demonstrate analytically, numerically, and experimentally that at sufficiently large driving currents and for a spin polarization direction tilted away from the normal to a nanocontact plane, the circular droplet soliton can become unstable against the excitations in the form of periodic deformations of its perimeter. We also show that these perimeter excitation modes (PEMs) can be excited parametrically when the fundamental droplet soliton precession frequency is close to the double frequency of one of the PEMs. As a consequence, with increasing magnitude of a bias magnetic field the PEMs with progressively higher indices and frequencies can be excited. Full qualitative and partly quantitative agreement with experiment confirm the presented theoretical picture.

  • 344.
    Xing, Xiangjun
    et al.
    Guangdong Univ Technol, Sch Phys & Optoelect Engn, Guangzhou 510006, Peoples R China..
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Gothenburg, Dept Phys, Fysikgrand 3, S-41296 Gothenburg, Sweden.
    Zhou, Yan
    Chinese Univ Hong Kong, Sch Sci & Engn, Shenzhen 518172, Guangdong, Peoples R China..
    Enhanced skyrmion motion via strip domain wall2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 21, article id 214432Article in journal (Refereed)
    Abstract [en]

    When magnetic skyrmions move under spin-orbit torque in magnetic nanowires, they experience a skyrmion Hall effect, which pushes them towards the nanowire edge where they risk being annihilated; this puts an upper limit on how fast they can be driven. However, the same magnetic multilayer harboring skyrmions can sustain a Neel-type strip domain wall along the nanowire length, potentially keeping the skyrmions separated from the edge. Here we study the interplay between current driven skyrmions and domain walls and find that they increase the annihilation current and allow the skyrmions to move faster. Based on the Thiele formalism, we confirm that the emergent longitudinal repulsive force and the modified energy landscape linked to the domain wall are responsible for the enhanced skyrmion motion. Furthermore, we identify that the longitudinal repulsive force emerges because of the broken axisymmetry in the local magnetization in front of the skyrmion. Our study uncovers key aspects in the interplay between two topological magnetic textures from different homotopy groups and may inspire new device concepts.

  • 345.
    Xypakis, Emmanouil
    et al.
    Max Planck Inst Phys Komplexer Syst, D-01187 Dresden, Germany..
    Rhim, Jun-Won
    Max Planck Inst Phys Komplexer Syst, D-01187 Dresden, Germany.;Inst for Basic Sci Korea, Ctr Correlated Electron Syst, Seoul 08826, South Korea.;Seoul Natl Univ, Dept Phys & Astron, Seoul 08826, South Korea..
    Bardarson, Jens H.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory. Max Planck Inst Phys Komplexer Syst, D-01187 Dresden, Germany.
    Ilan, Roni
    Tel Aviv Univ, Raymond & Beverly Sackler Sch Phys & Astron, IL-69978 Tel Aviv, Israel..
    Perfect transmission and Aharanov-Bohm oscillations in topological insulator nanowires with nonuniform cross section2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 4, article id 045401Article in journal (Refereed)
    Abstract [en]

    Topological insulator nanowires with uniform cross section, combined with a magnetic flux, can host both a perfectly transmitted mode and Majorana zero modes. Here we consider nanowires with rippled surfaces- specifically, wires with a circular cross section with a radius varying along its axis-and we calculate their transport properties. At zero doping, chiral symmetry places the clean wires (no impurities) in the AIII symmetry class, which results in a Z topological classification. A magnetic flux threading the wire tunes between the topologically distinct insulating phases, with perfect transmission obtained at the phase transition. We derive an analytical expression for the exact flux value at the transition. Both doping and disorder break the chiral symmetry and the perfect transmission. At finite doping, the interplay of surface ripples and disorder with the magnetic flux modifies quantum interference such that the amplitude of Aharonov-Bohm oscillations reduces with increasing flux, in contrast to wires with uniform surfaces where it is flux-independent.

  • 346.
    Yang, Qigui
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering. Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China.;Chinese Acad Sci, Inst High Energy Phys, China Spallat Neutron Source, Dongguan 523803, Peoples R China.
    Cao, Xingzhong
    Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China.
    Wang, Baoyi
    Chinese Acad Sci, Inst High Energy Phys, Beijing 100049, Peoples R China.
    Wang, Ping
    Chinese Acad Sci, Inst High Energy Phys, China Spallat Neutron Source, Dongguan 523803, Peoples R China.
    Systematic investigation of positron annihilation in transition metals from first principles2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, no 10, article id 104113Article in journal (Refereed)
    Abstract [en]

    In this work, we present a systematic theoretical study on the positron annihilation characteristics (positron lifetimes and momentum distributions) in transition metals (3d, 4d, and 5d metals) and other elements (carbon, aluminum, silicon, and phosphorus). Our calculations agree well with available reference experimental and theoretical data. We show that clear patterns exist in the evolution of the positron annihilation characteristics in pure elements. The evolution of momentum distribution in one transition metal series is mainly contributed by the filling of d-band electrons. For the positron lifetimes, the lifetimes of transition metals evolve with their d-band filling in a similar behavior as their atomic volumes. A case study is performed to show qualitatively the effect of solute elements on the Doppler spectra of defects. It is demonstrated that vacancy-solute complexes depict similar annihilation characteristics as the corresponding pure solute elements, meaning that vacancy-solute complexes can be reliably identified if the Doppler spectra of the pure solute elements are known. For the positron lifetimes, we found that they have a linear relation with the atomic volumes of elements for the same transition metal series. This work is expected to improve understanding of the positron annihilation characteristics of transition metals. The results could be used to investigate and identify the microstructures in alloys and compounds, such as vacancy-solute complexes, solute clusters, precipitates, and vacancies in different sublattices of compounds.

  • 347.
    Yuan, Ya-Hua
    et al.
    Cent South Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Duan, Yu-Xia
    Cent South Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Rusz, Jan
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Zhang, Chen
    Cent South Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Song, Jiao-Jiao
    Cent South Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Wu, Qi-Yi
    Cent South Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Sassa, Yasmine
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden.;Chalmers Univ Technol, Dept Phys, S-41296 Gothenburg, Sweden..
    Tjernberg, Oscar
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Berntsen, Magnus H.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Wu, Fan-Ying
    Cent South Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Liu, Shu-Yu
    Cent South Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Liu, Hao
    Cent South Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Zhu, Shuang-Xing
    Cent South Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Liu, Zi-Teng
    Cent South Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Zhao, Yin-Zou
    Cent South Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Tobash, P. H.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Bauer, Eric D.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Thompson, Joe D.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Oppeneer, Peter M.
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Durakiewicz, Tomasz
    Marie Curie Sklodowska Univ, Inst Phys, PL-20031 Lublin, Poland..
    Meng, Jian-Qiao
    Cent South Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Angle-resolved photoemission spectroscopy view on the nature of Ce 4f electrons in the antiferromagnetic Kondo lattice CePd5Al22021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, no 12, article id 125122Article in journal (Refereed)
    Abstract [en]

    We report an angle-resolved photoemission spectroscopy study of the antiferromagnetic Kondo lattice CePd5Al2, focusing on the quasi-two-dimensional k-space nature of its Fermi surface and, tuning photon energy to the Ce 4d-4f on-resonance transition, the hybridization of the Ce 4f state. A strong shoulder feature on the f(0) peak was detected, suggesting hybridization between conduction and f bands. On-resonance spectra revealed narrow, yet hybridized quasiparticle bands with sharp peaks and similar to 9 meV energy dispersion near the Fermi energy EF. The observed dispersive hybridized f band can be well described by a hybridization-band picture based on the periodic Anderson model (PAM). Hence, the 4f electrons in CePd5Al2 display a dual nature, with both localized and itinerant features, but with dominantly localized character.

  • 348.
    Zhang, Chen
    et al.
    School of Physics, Central South University, Changsha 410083, Hunan, People's Republic of China, Hunan.
    Yuan, Ya Hua
    School of Physics, Central South University, Changsha 410083, Hunan, People's Republic of China, Hunan.
    Song, Jiao Jiao
    School of Physics, Central South University, Changsha 410083, Hunan, People's Republic of China, Hunan.
    Rusz, Ján
    Department of Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden, Box 516.
    Zhao, Yin Zou
    School of Physics, Central South University, Changsha 410083, Hunan, People's Republic of China, Hunan.
    Wu, Qi Yi
    School of Physics, Central South University, Changsha 410083, Hunan, People's Republic of China, Hunan.
    Duan, Yu Xia
    School of Physics, Central South University, Changsha 410083, Hunan, People's Republic of China, Hunan.
    Sassa, Yasmine
    Department of Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden, Box 516; Department of Physics, Chalmers University of Technology, 41296 Göteborg, Sweden.
    Tjernberg, Oscar
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. KTH, School of Engineering Sciences (SCI), Applied Physics. Department of Applied Physics, KTH Royal Institute of Technology, Electrum 229, SE-16440, Stockholm, Kista, Sweden, Electrum 229, Kista.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Berntsen, Magnus H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Tobash, P. H.
    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
    Bauer, Eric D.
    Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
    Oppeneer, Peter M.
    Department of Physics and Astronomy, Uppsala University, Box 516, S-75120 Uppsala, Sweden, Box 516.
    Durakiewicz, Tomasz
    Idaho National Laboratory, Idaho Falls, Idaho 83415 USA.
    Meng, Jian Qiao
    School of Physics, Central South University, Changsha 410083, Hunan, People's Republic of China, Hunan.
    Antiferromagnetic order in Kondo lattice CePd5Al2 possibly driven by nesting2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, no 3, article id 035108Article in journal (Refereed)
    Abstract [en]

    We investigated the electronic structure of the antiferromagnetic Kondo lattice CePd5Al2 using high-resolution angle-resolved photoemission spectroscopy. The experimentally determined band structure of the conduction electrons is predominated by the Pd 4d character. It contains multiple hole and electron Fermi pockets, in good agreement with density functional theory calculations. The Fermi surface is folded over Q0=(0,0,1), manifested by Fermi surface reconstruction and band folding. Our results suggest that Fermi surface nesting drives the formation of antiferromagnetic order in CePd5Al2.

  • 349.
    Zhu, Li-Fang
    et al.
    Max Planck Inst Eisenforsch GmbH, Dept Computat Mat Design, Max Planck Str 1, D-40237 Dusseldorf, Germany..
    Koermann, Fritz
    Max Planck Inst Eisenforsch GmbH, Dept Computat Mat Design, Max Planck Str 1, D-40237 Dusseldorf, Germany.;Delft Univ Technol, Dept Mat Sci & Engn, Mekelweg 2, NL-2628 CD Delft, Netherlands..
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Mat Ctr Leoben, A-8700 Leoben, Austria..
    Neugebauer, Joerg
    Max Planck Inst Eisenforsch GmbH, Dept Computat Mat Design, Max Planck Str 1, D-40237 Dusseldorf, Germany..
    Grabowski, Blazej
    Univ Stuttgart, Inst Mat Sci, Pfaffenwaldring 55, D-70569 Stuttgart, Germany..
    Performance of the standard exchange-correlation functionals in predicting melting properties fully from first principles: Application to Al and magnetic Ni2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 14, article id 144108Article in journal (Refereed)
    Abstract [en]

    We apply the efficient two-optimized references thermodynamic integration using Langevin dynamics method [Phys. Rey. B 96, 224202 (2017)] to calculate highly accurate melting properties of Al and magnetic Ni from first principles. For Ni we carefully investigate the impact of magnetism on the liquid and solid free energies including longitudinal spin fluctuations and the reverse influence of atomic vibrations on magnetic properties. We show that magnetic fluctuations are effectively canceling out for both phases and are thus not altering the predicted melting temperature. For both elements, the generalized gradient approximation (GGA) and the local-density approximation (LDA) are used for the exchange-correlation functional revealing a reliable ab initio confidence interval capturing the respective experimental melting point, enthalpy of fusion, and entropy of fusion.

  • 350.
    Zyuzin, Alexander A.
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Zyuzin, A. Yu.
    Flat band in disorder-driven non-Hermitian Weyl semimetals2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 4, article id 041203Article in journal (Refereed)
    Abstract [en]

    We study the interplay of disorder and band-structure topology in a Weyl semimetal with a tilted conical spectrum around the Weyl points. The spectrum of particles is given by the eigenvalues of a non-Hermitian matrix, which contains contributions from a Weyl Hamiltonian and complex self-energy due to electron elastic scattering on disorder. We find that the tilt-induced matrix structure of the self-energy gives rise to either a flat band or a nodal line segment at the interface of the electron and hole pockets in the bulk band structure of type-II Weyl semimetals depending on the Weyl cone inclination. For the tilt in a single direction in momentum space, each Weyl point expands into a flat band lying on the plane, which is transverse to the direction of the tilt. The spectrum of the flat band is fully imaginary and is separated from the in-plane dispersive part of the spectrum by the "exceptional nodal ring" where the matrix of the Green's function in momentum-frequency space is defective. The tilt in two directions might shrink a flat band into a nodal line segment with "exceptional edge points." We discuss the connection to the non-Hermitian topological theory.

45678 301 - 350 of 353
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