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  • 101. Gao, S.
    et al.
    Guratinder, K.
    Stuhr, U.
    White, J. S.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics. Paul Scherrer Institute, Villigen, Switzerland.
    Roessli, B.
    Fennell, T.
    Tsurkan, V.
    Loidl, A.
    Ciomaga Hatnean, M.
    Balakrishnan, G.
    Raymond, S.
    Chapon, L.
    Garlea, V. O.
    Savici, A. T.
    Cervellino, A.
    Bombardi, A.
    Chernyshov, D.
    Rüegg, C.
    Haraldsen, J. T.
    Zaharko, O.
    Manifolds of magnetic ordered states and excitations in the almost Heisenberg pyrochlore antiferromagnet MgCr2 O42018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 13, article id 134430Article in journal (Refereed)
    Abstract [en]

    In spinels ACr2O4(A=Mg, Zn), realization of the classical pyrochlore Heisenberg antiferromagnet model is complicated by a strong spin-lattice coupling: the extensive degeneracy of the ground state is lifted by a magneto-structural transition at TN=12.5 K. We study the resulting low-temperature low-symmetry crystal structure by synchrotron x-ray diffraction. The consistent features of x-ray low-temperature patterns are explained by the tetragonal model of Ehrenberg et al. [Pow. Diff. 17, 230 (2002)PODIE20885-715610.1154/1.1479738], while other features depend on sample or cooling protocol. A complex, partially ordered magnetic state is studied by neutron diffraction and spherical neutron polarimetry. Multiple magnetic domains of configuration arms of the propagation vectors k1=(12120),k2=(1012) appear. The ordered moment reaches 1.94(3) μB/Cr3+ for k1 and 2.08(3) μB/Cr3+ for k2, if equal amount of the k1 and k2 phases is assumed. The magnetic arrangements have the dominant components along the [110] and [1-10] diagonals and a smaller c component. We use inelastic neutron scattering to investigate the spin excitations, which comprise a mixture of dispersive spin waves propagating from the magnetic Bragg peaks and resonance modes centered at equal energy steps of 4.5 meV. We interpret these as acoustic and optical spin wave branches, but show that the neutron scattering cross sections of transitions within a unit of two corner-sharing tetrahedra match the observed intensity distribution of the resonances. The distinctive fingerprint of clusterlike excitations in the optical spin wave branches suggests that propagating excitations are localized by the complex crystal structure and magnetic orders.

  • 102.
    Garaud, Julien
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Statistical Physics.
    Bojesen, Troels Arnfred
    Sudbo, Asle
    Lattices of double-quanta vortices and chirality inversion in p(x) + i p(y) superconductors2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 10, article id 104509Article in journal (Refereed)
    Abstract [en]

    We investigate the magnetization processes of a standard Ginzburg-Landau model for chiral p-wave superconducting states in an applied magnetic field. We find that the phase diagram is dominated by triangular lattices of doubly quantized vortices. Only in close vicinity to the upper critical field the lattice starts to dissociate into a structure of single-quanta vortices. The degeneracy between states with opposite chirality is broken in a nonzero field. If the magnetization starts with an energetically unfavorable chirality, the process of chirality inversion induced by the external magnetic field results in the formation of a sequence of metastable states with characteristic magnetic signatures that can be probed by standard experimental techniques.

  • 103.
    Garaud, Julien
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Corticelli, Alberto
    KTH, School of Engineering Sciences (SCI), Physics.
    Silaev, Mihail
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Physics.
    Field-induced coexistence of s(++) and s(+/-) superconducting states in dirty multiband superconductors2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 5, article id 054520Article in journal (Refereed)
    Abstract [en]

    In multiband systems, such as iron-based superconductors, the superconducting states with locking and antilocking of the interband phase differences are usually considered as mutually exclusive. For example, a dirty two-band system with interband impurity scattering undergoes a sharp crossover between the s(+/-) state (which favors phase antilocking) and the s(++) state (which favors phase locking). We discuss here that the situation can be much more complex in the presence of an external field or superconducting currents. In an external applied magnetic field, dirty two-band superconductors do not feature a sharp s(perpendicular to) -> s(++) crossover but rather awashed-out crossover to a finite region in the parameter space where both s(+/-) and s(++) states can coexist for example as a lattice or a microemulsion of inclusions of different states. The current-carrying regions such as the regions near vortex cores can exhibit an s(+/-) state while it is the s(++) state that is favored in the bulk. This coexistence of both states can even be realized in the Meissner state at the domain's boundaries featuring Meissner currents. We demonstrate that there is a magnetic-field-driven crossover between the pure s(+/-) and the s(++) states.

  • 104.
    Garaud, Julien
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Corticelli, Alberto
    KTH, School of Engineering Sciences (SCI), Physics.
    Silaev, Mihail
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Physics, Statistical Physics.
    Properties of dirty two-band superconductors with repulsive interband interaction: Normal modes, length scales, vortices, and magnetic response2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 1, article id 014520Article in journal (Refereed)
    Abstract [en]

    Disorder in two-band superconductors with repulsive interband interaction induces a frustrated competition between the phase-locking preferences of the various potential and kinetic terms. This frustrated interaction can result in the formation of an s + is superconducting state that breaks the time-reversal symmetry. In this paper we study the normal modes and their associated coherence lengths in such materials. We especially focus on the consequences of the soft modes stemming from the frustration and time-reversal symmetry breakdown. We find that two-band superconductors with such impurity-induced frustrated interactions display a rich spectrum of physical properties that are absent in their clean counterparts. It features a mixing of Leggett's and Anderson-Higgs modes, and a soft mode with diverging coherence length at the impurity-induced second-order phase transition from s +/- / s ++ states to the s + is state. Such a soft mode generically results in long-range attractive intervortex forces that can trigger the formation of vortex clusters. We find that, if such clusters are formed, their size and internal flux density have a characteristic temperature dependence that could be probed in muon-spin-rotation experiments. We also comment on the appearance of spontaneous magnetic fields due to spatially varying impurities.

  • 105.
    Garaud, Julien
    et al.
    Institut Denis Poisson CNRS/UMR 7013, Université de Tours, 37200 France.
    Korneev, Anatolii
    Pacific Quantum Center, Far Eastern Federal University, Sukhanova 8, Vladivostok 690950, Russia, Sukhanova 8.
    Samoilenka, Albert
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Molochkov, Alexander
    Pacific Quantum Center, Far Eastern Federal University, Sukhanova 8, Vladivostok 690950, Russia, Sukhanova 8.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Chernodub, Maxim
    Institut Denis Poisson CNRS/UMR 7013, Université de Tours, 37200 France.
    Counterpart of the Chandrasekhar-Kendall state in noncentrosymmetric superconductors2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, no 1, article id 014504Article in journal (Refereed)
    Abstract [en]

    We demonstrate that superconductors with broken inversion symmetry support a family of stable, spatially localized configurations of the self-knotted magnetic field. These solutions, which we term “toroflux,” are the superconducting counterparts of the Chandrasekhar-Kendall states (spheromaks) that appear in highly conducting, force-free astrophysical and nuclear-fusion plasmas. The superconducting torofluxes are solutions of superconducting models, in the presence of a parity-breaking Lifshitz invariant associated with the Formula Presented point-group symmetry. These solutions are characterized by a nonvanishing helicity of the magnetic field, and also by a toroidal dipole moment of the magnetic field. We demonstrate that a magnetic dipole or a ferromagnetic inclusion in the bulk of a noncentrosymmetric superconductor sources finite-energy toroflux solutions.

  • 106.
    Garaud, Julien
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Silaev, Mihail
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Physics, Statistical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Change of the vortex core structure in two-band superconductors at the impurity-scattering-driven s(+/-)/s(++) crossover2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 14, article id 140503Article in journal (Refereed)
  • 107.
    Garmroudi, F.
    et al.
    Tech Univ Wien, Inst Solid State Phys, A-1040 Vienna, Austria..
    Parzer, M.
    Tech Univ Wien, Inst Solid State Phys, A-1040 Vienna, Austria..
    Knopf, M.
    Tech Univ Wien, Inst Solid State Phys, A-1040 Vienna, Austria..
    Riss, A.
    Tech Univ Wien, Inst Solid State Phys, A-1040 Vienna, Austria..
    Michor, H.
    Tech Univ Wien, Inst Solid State Phys, A-1040 Vienna, Austria..
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures. Mat Ctr Leoben Forsch GmbH, A-8700 Leoben, Austria..
    Mori, T.
    Natl Inst Mat Sci, Int Ctr Mat Nanoarchitecton WPI MANA, Tsukuba 3050044, Japan.;Univ Tsukuba, Tsukuba 3058577, Japan..
    Bauer, E.
    Tech Univ Wien, Inst Solid State Phys, A-1040 Vienna, Austria..
    Unveiling the structure-property relationship in metastable Heusler compounds by systematic disorder tuning2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 1, article id 014108Article in journal (Refereed)
    Abstract [en]

    Heusler compounds represent a unique class of materials that exhibit a wide range of fascinating and tuneable properties such as exotic magnetic phases, superconductivity, band topology, or thermoelectricity. An exceptional, but for Heusler compounds common, feature is that they are prone to antisite defects and disorder. In this regard, the Fe2VAl Heusler compound has been a particularly interesting and disputed candidate. Even though various theoretical scenarios for the interplay of physical properties and disorder have been proposed, the metastable disordered A2 phase hitherto precluded experimental investigation in bulk samples. Here, we report experimental results on disorder-tuned Fe2VAl0.9Si0.1 alloys all the way toward the A2 phase, which we realized via rapidly quenching our samples from high temperatures. We measured the thermoelectric properties of these materials in a wide temperature range (4 to 700 K); they suggest a gradual semimetal/narrow-gap semiconductor -> metal transition upon increasing the disorder. We also find a large anomalous Hall effect in the disordered A2 phase, arising from the side-jump scattering of charge carriers at the antisite magnetic moments. This is corroborated by measurements of the temperature-and field-dependent magnetization, which increases dramatically up to approximate to 2.5 mu B/f.u. as compared to the ordered compound (<0.1 mu B/f.u.). This study provides an experimental realization of the metastable A2 structure in bulk Fe2VAl-based alloys and grants insight into the structure-property relationship of these materials. Our work confirms that temperature-induced antisite disorder, occurring during thermal heat treatment, can be a precisely tuneable parameter in the family of Heusler compounds.

  • 108.
    Gebresenbut, Girma Hailu
    et al.
    Uppsala Univ, Angstrom Lab, Dept Chem, Box 538, S-75121 Uppsala, Sweden..
    Shiino, Takayuki
    Uppsala Univ, Dept Mat Sci & Engn, Box 35, S-75103 Uppsala, Sweden..
    Andersson, Mikael Svante
    Uppsala Univ, Angstrom Lab, Dept Chem, Box 538, S-75121 Uppsala, Sweden..
    Qureshi, Navid
    Inst Laue Langevin, CS 20156, 71 Ave Martyrs, F-38042 Grenoble, France.;European Spallat Source ESS ERIC, Box 176, S-22100 Lund, Sweden..
    Fabelo, Oscar
    Inst Laue Langevin, CS 20156, 71 Ave Martyrs, F-38042 Grenoble, France.;European Spallat Source ESS ERIC, Box 176, S-22100 Lund, Sweden..
    Beran, Premysl
    Nucl Phys Inst CAS, Hlavni 160, Husinec 25068, Czech Republic..
    Qvarngard, Daniel
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Henelius, Patrik
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory. Abo Akad Univ, Fac Sci & Engn, Turku 20500, Finland..
    Rydh, Andreas
    Stockholm Univ, Dept Phys, SE-10691 Stockholm, Sweden..
    Mathieu, Roland
    Uppsala Univ, Dept Mat Sci & Engn, Box 35, S-75103 Uppsala, Sweden..
    Nordblad, Per
    Uppsala Univ, Dept Mat Sci & Engn, Box 35, S-75103 Uppsala, Sweden..
    Gomez, Cesar Pay
    Uppsala Univ, Angstrom Lab, Dept Chem, Box 538, S-75121 Uppsala, Sweden..
    Effect of pseudo-Tsai cluster incorporation on the magnetic structures of R-Au-Si (R = Tb, Ho) quasicrystal approximants2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, no 18, article id 184413Article in journal (Refereed)
    Abstract [en]

    In cluster-based quasicrystals, tetrahedra located in conventional Tsai clusters may be replaced by single rare-earth (R) ions at the cluster centers (pseudo-Tsai clusters). In this study, we investigate the effect of the pseudo-Tsai cluster incorporation on the magnetic structures of two approximants, the Tsai-type Tb-Au-Si [denoted TAS(0)] and Ho-Au-Si [denoted HAS(52)] with partial replacement of conventional Tsai clusters by pseudo-Tsai clusters, up to 52%. The mixture of Tsai and pseudo-Tsai clusters can be considered a different source of randomness/disorder other than the conventional chemical mix sites (Au/Si). The effect of the latter has been previously discussed regarding the origin/cause of spin-glass-like ordering and Anderson localization of electronic states in quasicrystals and approximant crystals. Single crystal neutron diffraction experiments at 2 K were performed and bulk physical properties (magnetization and specific heat) were investigated. In addition, earlier collected powder neutron diffraction data of TAS(14) with 14% replacement was reanalyzed in light of the results on TAS(0) and HAS(52). We find that the arrangement of ordered magnetic spins in the icosahedral shells of these phases is similar, while the cluster-center R magnetic states are different. In the case of TAS(14), the cluster-center Tb magnetic moments seem to affect the arrangement of surrounding icosahedral magnetic moments, and the magnetic structure of the icosahedral shell deviates from that of TAS(0). In the case of HAS(52), however, the icosahedral R magnetic moments are less affected by the cluster-center R, while the averaged cluster-center R magnetic moments are significantly diminished. We discuss these results considering the magnetic ordering effect on the bulk physical properties.

  • 109.
    Geilhufe, Matthias
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Institute for Materials Science, Los Alamos National Laboratory, Los Alamos, USA; Department of Physics, University of Connecticut, USA.
    Symmetry analysis of odd- and even-frequency superconducting gap symmetries for time-reversal symmetric interactions2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 2, article id 024507Article in journal (Refereed)
    Abstract [en]

    Odd-frequency superconductivity describes a class of superconducting states where the superconducting gap is an odd function in relative time and Matsubara frequency. We present a group theoretical analysis based on the linearized gap equation in terms of Shubnikov groups of the second kind. By discussing systems with spin-orbit coupling and an interaction kernel which is symmetric under the reversal of relative time, we show that both even-and odd-frequency gaps are allowed to occur. Specific examples are discussed for the square lattice, the octahedral lattice, and the tetragonal lattice. For irreducible representations that are even under the reversal of relative time the common combinations of s- and d-wave spin singlet and p-wave spin triplet gaps are revealed, irreducible representations that are odd under reversal of relative time give rise to s- and d-wave spin triplet and p-wave spin singlet gaps. Furthermore, we discuss the construction of a generalized Ginzburg-Landau theory in terms of the associated irreducible representations. The result complements the established classification of superconducting states of matter.

  • 110.
    Geilhufe, Matthias
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden.
    Guinea, Francisco
    Imdea Nanosci, Faraday 9, Madrid 28015, Spain.;Univ Manchester, Sch Phys & Astron, Manchester M13 9PY, Lancs, England..
    Juricic, Vladimir
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden.
    Hund nodal line semimetals: The case of a twisted magnetic phase in the double-exchange model2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 2, article id 020404Article in journal (Refereed)
    Abstract [en]

    We propose a class of topological metals, which we dub Hund nodal line semimetals, arising from the strong Coulomb interaction encoded in the Hund's coupling between itinerant electrons and localized spins. We here consider a particular twisted spin configuration, which is realized in the double-exchange model which describes the manganite oxides. The resulting effective tetragonal lattice of electrons with hoppings tied to the local spin features an antiunitary nonsymmorphic symmetry that, in turn, together with another nonsymmorphic but unitary glide-mirror symmetry, protects crossings of a double pair of bands along a high-symmetry line on the Brillouin zone boundary. We also discuss the stability of Hund nodal line semimetals with respect to symmetry breaking arising from various perturbations of the twisted phase. Our results motivate further studies of other realizations of this state of matter, for instance, in different spin backgrounds, properties of its drumhead surface states, as well as its stability to disorder and interactions among the itinerant electrons.

  • 111.
    Geilhufe, Matthias
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Olsthoorn, Bart
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Identification of strongly interacting organic semimetals2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, no 20, article id 205134Article in journal (Refereed)
    Abstract [en]

    Dirac and Weyl point- and line-node semimetals are characterized by a zero band gap with simultaneously vanishing density of states. Given a sufficient interaction strength, such materials can undergo an interaction instability, e.g., into an excitonic insulator phase. Due to generically flatbands, organic crystals represent a promising materials class in this regard. We combine machine learning, density functional theory, and effective models to identify specific example materials. Without taking into account the effect of many-body interactions, we found the organic charge transfer salts [bis(3,4-diiodo-3',4'-ethyleneditio-tetrathiafulvalene), 2,3-dichloro-5,6-dicyanobenzoquinone, acetenitrile] [(EDT-TTF-I-2)(2)](DDQ)center dot(CH3CN) and 2, 2', 5, 5'-tetraselenafulvalene-7, 7, 8, 8-tetracyano-p-quinodimethane (TSeF-TCNQ) and a bis-1,2,3-dithiazolyl radical conductor to exhibit a semimetallic phase in our ab initio calculations. Adding the effect of strong particle-hole interactions for (EDT-TTF-I-2)(2)(DDQ)center dot(CH3CN) and TSeF-TCNQ opens an excitonic gap on the order of 60 and 100 meV, which is in good agreement with previous experiments on these materials.

  • 112.
    Geilhufe, R. Matthias
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Bouhon, Adrien
    Borysov, Stanislav S.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Three-dimensional organic Dirac-line materials due to nonsymmorphic symmetry: A data mining approach2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 4, article id 041103Article in journal (Refereed)
    Abstract [en]

    A datamining study of electronic Kohn-Sham band structures was performed to identify Dirac materials within the Organic Materials Database. Out of that, the three-dimensional organic crystal 5,6-bis(trifluoromethyl)-2-methoxy-1H-1,3-diazepine was found to host different Dirac-line nodes within the band structure. From a group theoretical analysis, it is possible to distinguish between Dirac-line nodes occurring due to twofold degenerate energy levels protected by the monoclinic crystalline symmetry and twofold degenerate accidental crossings protected by the topology of the electronic band structure. The obtained results can be generalized to all materials having the space group P2(1)/c (No. 14, C-2h(5)) by introducing three distinct topological classes.

  • 113.
    Ghorai, Sagar
    et al.
    Uppsala Univ, Dept Mat Sci & Engn, Box 35, SE-75103 Uppsala, Sweden..
    Cedervall, Johan
    Stockholm Univ, Dept Mat & Environm Chem, SE-10691 Stockholm, Sweden..
    Clulow, Rebecca
    Uppsala Univ, Dept Chem, Angstrom Lab, Box 538, SE-75121 Uppsala, Sweden..
    Huang, Shuo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. China Univ Geosci, Fac Mat Sci & Chem, Wuhan 430074, Peoples R China..
    Ericsson, Tore
    Uppsala Univ, Dept Chem, Angstrom Lab, Box 538, SE-75121 Uppsala, Sweden..
    Haggstrom, Lennart
    Uppsala Univ, Dept Chem, Angstrom Lab, Box 538, SE-75121 Uppsala, Sweden..
    Shtender, Vitalii
    Uppsala Univ, Dept Chem, Angstrom Lab, Box 538, SE-75121 Uppsala, Sweden..
    Delczeg-Czirjak, Erna K.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Eriksson, Olle
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Sahlberg, Martin
    Uppsala Univ, Dept Chem, Angstrom Lab, Box 538, SE-75121 Uppsala, Sweden..
    Svedlindh, Peter
    Uppsala Univ, Dept Mat Sci & Engn, Box 35, SE-75103 Uppsala, Sweden..
    Site-specific atomic substitution in a giant magnetocaloric Fe2P-type system2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 10, article id 104409Article in journal (Refereed)
    Abstract [en]

    Giant magnetocaloric (GMC) materials constitute a requirement for near-room-temperature magnetic re-frigeration. (Fe,Mn)2(P,Si) is a GMC compound with strong magnetoelastic coupling. The main hindrance towards application of this material is a comparably large temperature hysteresis, which can be reduced by metal site substitution with a nonmagnetic element. However, the (Fe,Mn)2(P,Si) compound has two equally populated metal sites, the tetrahedrally coordinated 3 f and the pyramidally coordinated 3g sites. The magnetic and magnetocaloric properties of such compounds are highly sensitive to the site-specific occupancy of the magnetic atoms. Here we have attempted to study separately the effect of 3 f and 3g site substitution with equal amounts of vanadium. Using formation energy calculations, the site preference of vanadium and its influence on the magnetic phase formation are described. A large difference in the isothermal entropy change (as high as 44%) with substitution in the 3 f and 3g sites is observed. The role of the lattice parameter change with temperature and the strength of the magnetoelastic coupling on the magnetic properties are highlighted.

  • 114.
    Ghosh, Anirudha
    et al.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Lund Univ, MAXLab 4, POB 118, S-22100 Lund, Sweden..
    Joensson, H. Johan M.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Asia Pacific Ctr Theoret Phys, Pohang 37673, South Korea..
    Mukkattukavil, Deepak John
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Kvashnin, Yaroslav
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Phuyal, Dibya
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Thunstroem, Patrik
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Agaker, Marcus
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Lund Univ, MAXLab 4, POB 118, S-22100 Lund, Sweden..
    Nicolaou, Alessandro
    Synchrotron SOLEIL, Orme Merisiers, BP48, F-91192 Gif Sur Yvette, France..
    Jonak, Martin
    Heidelberg Univ, Kirchhoff Inst Phys, D-69120 Heidelberg, Germany..
    Klingeler, Ruediger
    Heidelberg Univ, Kirchhoff Inst Phys, D-69120 Heidelberg, Germany..
    Kamalakar, M. Venkata
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Sarkar, Tapati
    Uppsala Univ, Dept Mat Sci & Engn, Box 35, S-75103 Uppsala, Sweden..
    Vasiliev, Alexander N.
    Natl Univ Sci & Tech MISS, Moscow 119049, Russia.;Lomonosov Moscow State Univ, Moscow 119991, Russia.;Ural Fed Univ, Ekaterinburg 620002, Russia..
    Butorin, Sergei M.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Eriksson, Olle
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Örebro Univ, Sch Sci & Technol, S-70182 Örebro, Sweden..
    Abdel-Hafiez, Mahmoud
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Univ Doha Sci & Technol, POB 24449, Doha, Qatar..
    Magnetic circular dichroism in the dd excitation in the van der Waals magnet CrI3 probed by resonant inelastic x-ray scattering2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 11, article id 115148Article in journal (Refereed)
    Abstract [en]

    We report on a combined experimental and theoretical study on CrI3 single crystals by employing the polarization dependence of resonant inelastic x-ray scattering (RIXS). Our investigations reveal multiple Cr 3d orbital splitting (dd excitations) as well as magnetic dichroism (MD) in the RIXS spectra. The dd excitation energies are similar on the two sides of the ferromagnetic transition temperature, T-C similar to 61 K, although MD in RIXS is predominant at 0.4 T magnetic field below TC. This demonstrates that the ferromagnetic superexchange interaction that is responsible for the interatomic exchange field is vanishingly small compared with the local exchange field that comes from exchange and correlation interaction among the interacting Cr 3d orbitals. The recorded RIXS spectra reported here reveal clearly resolved Cr 3d intraorbital dd excitations that represent transitions between electronic levels that are heavily influenced by dynamic correlations and multiconfiguration effects. Our calculations taking into account the Cr 3d hybridization with the ligand valence states and the full multiplet structure due to intra-atomic and crystal field interactions in Oh and D3d symmetry clearly reproduced the dichroic trend in experimental RIXS spectra.

  • 115.
    Gonçalves, Miguel
    et al.
    CeFEMA-LaPMET, Departamento de Física, Instituto Superior Técnico, Universidade de Lisboa, Avenida Rovisco Pais, 1049-001 Lisboa, Portugal, Avenida Rovisco Pais; Centro de Física das Universidades do Minho e Porto, Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, 4169-007 Porto, Portugal.
    Ribeiro, Pedro
    CeFEMA-LaPMET, Departamento de Física, Instituto Superior Técnico, Universidade de Lisboa, Avenida Rovisco Pais, 1049-001 Lisboa, Portugal, Avenida Rovisco Pais; Beijing Computational Science Research Center, Beijing 100193, China.
    Khaymovich, Ivan M.
    Nordita SU; Institute for Physics of Microstructures, Russian Academy of Sciences, 603950 Nizhny Novgorod, GSP-105, Russia.
    Quasiperiodicity hinders ergodic Floquet eigenstates2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, no 10, article id 104201Article in journal (Refereed)
    Abstract [en]

    Quasiperiodic systems in one dimension can host nonergodic states, e.g., states localized in position or momentum. Periodic quenches within localized phases yield Floquet eigenstates of the same nature, i.e., spatially localized or ballistic. However, periodic quenches across these two nonergodic phases were thought to produce ergodic diffusivelike states even for noninteracting particles. We show that this expectation is not met at the thermodynamic limit where the system always attains a nonergodic state. We find that ergodicity may be recovered by scaling the Floquet quenching period with system size and determine the corresponding scaling function. Our results suggest that, while the fraction of spatially localized or ballistic states depends on the model's details, all Floquet eigenstates belong to one of these nonergodic categories. Our findings demonstrate that quasiperiodicity hinders ergodicity and thermalization, even in driven systems where these phenomena are commonly expected.

  • 116.
    Gupta, Rahul
    et al.
    Uppsala Univ, Dept Engn Sci, Box 534, SE-75121 Uppsala, Sweden..
    Behera, Nilamani
    Uppsala Univ, Dept Engn Sci, Box 534, SE-75121 Uppsala, Sweden..
    Venugopal, Vijay A.
    Seagate Technol, 1 Disc Dr, Springtown BT48 0BF, North Ireland..
    Basu, Swaraj
    Seagate Technol, 1 Disc Dr, Springtown BT48 0BF, North Ireland..
    Puri, Anil K.
    Seagate Technol, 1 Disc Dr, Springtown BT48 0BF, North Ireland..
    Strom, Petter
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Gubbins, Mark A.
    Seagate Technol, 1 Disc Dr, Springtown BT48 0BF, North Ireland..
    Bergqvist, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Brucas, Rimantas
    Uppsala Univ, Dept Engn Sci, Box 534, SE-75121 Uppsala, Sweden..
    Svedlindh, Peter
    Uppsala Univ, Dept Engn Sci, Box 534, SE-75121 Uppsala, Sweden..
    Kumar, Ankit
    Uppsala Univ, Dept Engn Sci, Box 534, SE-75121 Uppsala, Sweden..
    Engineering of spin mixing conductance at Ru/FeCo/Ru interfaces: Effect of Re doping2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 2, article id 024401Article in journal (Refereed)
    Abstract [en]

    We have deposited polycrystalline Re-doped (Fe65Co35)((100-x))Re-x (0 <= x <= 12.6 at. %) thin films grown under identical conditions and sandwiched between thin layers of Ru in order to study the phenomenon of spin pumping as a function of Re concentration. In-plane and out-of-plane ferromagnetic resonance spectroscopy results show an enhancement of the Gilbert damping with an increase in Re doping. We find 98% enhancement in the real part of effective spin mixing conductance [Re(g(eff)(up arrow down arrow))] with Re doping. Conversely, the Re(g(eff)(up arrow down arrow)) does not change with Re doping in Fe65Co35 thin films which are seeded and capped with Cu layers. The enhancement in Re(g(eff)(up arrow down arrow)) of Re-doped Fe65Co35 thin films sandwiched between thin layers of Ru is linked to the Re doping-induced change of the interface electronic structure in the nonmagnetic Ru layer. The saturation magnetization decreases 35% with increasing Re doping up to 12.6 at. %. This study opens a direction of tuning the spin mixing conductance in magnetic heterostructures by doping of the ferromagnetic layer, which is essential for the realization of energyefficient operation of spintronic devices.

  • 117. Haidar, M.
    et al.
    Durrenfeld, P.
    Ranjbar, M.
    Balinsky, M.
    Fazlali, M.
    Dvornik, M.
    Dumas, R. K.
    Khartsev, Sergiy
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. University of Gothenburg, Sweden.
    Controlling Gilbert damping in a YIG film using nonlocal spin currents2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 18, article id 180409Article in journal (Refereed)
    Abstract [en]

    We demonstrate the control of Gilbert damping in 65-nm-thick yttrium iron garnet (YIG) films using a spin-polarized current generated by a direct current through a nanocontact, spin filtered by a thin Co layer. The magnetodynamics of both the YIG and the Co layers can be excited by a pulse-modulated microwave current injected through the nanocontact and the response detected as a lock-in amplified voltage over the device. The spectra show three clear peaks, two associated with the ferromagnetic resonance (FMR) in each layer, and an additional Co mode with a higher wave vector proportional to the inverse of the nanocontact diameter. By varying the sign and magnitude of the direct nanocontact current, we can either increase or decrease the linewidth of the YIG FMR peak consistent with additional positive or negative damping being exerted by the nonlocal spin current injected into the YIG film. Our nanocontact approach thus offers an alternative route in the search for auto-oscillations in YIG films.

  • 118.
    Halcrow, Chris
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Ferroelectric domain wall clusters in perfectly screened barium titanate type systems2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, no 17, article id 174101Article in journal (Refereed)
    Abstract [en]

    We study ferroelectric domain walls in barium titanate-type systems with perfect electric screening. We search for structurally nontrivial so-called non-Ising domain walls, where the polarization is nontrivial for all components. Our approach enables us to find solutions for domain walls in any orientation, and the existence and energy of these walls depend on their particular orientation. We find that, across all phases of the material, there are orientations where the non-Ising walls have lower energy than Ising walls. The most interesting property of these domain walls is their nonmonotonic interaction forces, allowing them to form stable domain-wall clusters rather than following standard behavior where domain walls annihilate or repel each other. We find the required external electric field to create the non-Ising configurations. Besides theoretical interest, this unconventional property of domain walls makes them a good candidate for memory applications.

  • 119.
    Hannukainen, Julia D.
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Ferreiros, Yago
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory. IMDEA Nanociencia, Faraday 9, Madrid 28049, Spain..
    Cortijo, Alberto
    CSIC, Inst Ciencia Mat Madrid, Madrid 28049, Spain..
    Bardarson, Jens H.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Axial anomaly generation by domain wall motion in Weyl semimetals2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, no 24, article id 241401Article in journal (Refereed)
    Abstract [en]

    A space-time dependent node separation in Weyl semimetals acts as an axial vector field. Coupled with domain wall motion in magnetic Weyl semimetals, this induces axial electric and magnetic fields localized at the domain wall. We show how these fields can activate the axial (chiral) anomaly and provide a direct experimental signature of it. Specifically, a domain wall provides a spatially dependent Weyl node separation and an axial magnetic field B-5, and domain wall movement, driven by an external magnetic field, gives the Weyl node separation a time dependence, inducing an axial electric field E-5. At magnetic fields beyond the Walker breakdown, E-5. B-5 becomes nonzero and activates the axial anomaly that induces a finite axial charge density-imbalance in the number of left- and right-handed fermions-moving with the domain wall. This axial density in turn produces, via the chiral magnetic effect, an oscillating current flowing along the domain wall plane, resulting in a characteristic radiation of electromagnetic waves emanating from the domain wall. A detection of this radiation would constitute a direct measurement of the axial anomaly induced by axial electromagnetic fields.

  • 120. Hart, James L.
    et al.
    Liu, Shi
    Lang, Andrew C.
    Hubert, Alexander
    Zukauskas, Andrius
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Canalias, Carlota
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Beanland, Richard
    Rappe, Andrew M.
    Arredondo, Miryam
    Taheri, Mitra L.
    Electron-beam-induced ferroelectric domain behavior in the transmission electron microscope: Toward deterministic domain patterning2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 17, article id 174104Article in journal (Refereed)
    Abstract [en]

    We report on transmission electron microscope beam-induced ferroelectric domain nucleation and motion. While previous observations of this phenomenon have been reported, a consistent theory explaining induced domain response is lacking, and little control over domain behavior has been demonstrated. We identify positive sample charging, a result of Auger and secondary electron emission, as the underlying mechanism driving domain behavior. By converging the electron beam to a focused probe, we demonstrate controlled nucleation of nanoscale domains. Molecular dynamics simulations performed are consistent with experimental results, confirming positive sample charging and reproducing the result of controlled domain nucleation. Furthermore, we discuss the effects of sample geometry and electron irradiation conditions on induced domain response. These findings elucidate past reports of electron beam-induced domain behavior in the transmission electron microscope and provide a path towards more predictive, deterministic domain patterning through electron irradiation.

  • 121.
    Haugen, Havard Homleid
    et al.
    Norwegian Univ Sci & Technol, Dept Phys, NO-7491 Trondheim, Norway.;Norwegian Univ Sci & Technol, Dept Phys, Ctr Quantum Spintron, NO-7491 Trondheim, Norway..
    Babaev, Egor
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Krohg, Fredrik Nicolai
    Norwegian Univ Sci & Technol, Dept Phys, NO-7491 Trondheim, Norway.;Norwegian Univ Sci & Technol, Dept Phys, Ctr Quantum Spintron, NO-7491 Trondheim, Norway..
    Sudbo, Asle
    Norwegian Univ Sci & Technol, Dept Phys, NO-7491 Trondheim, Norway.;Norwegian Univ Sci & Technol, Dept Phys, Ctr Quantum Spintron, NO-7491 Trondheim, Norway..
    First-order superconducting phase transition in a chiral p plus ip system2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 10, article id 104515Article in journal (Refereed)
    Abstract [en]

    We use large-scale Monte Carlo computations to study the phase transitions between a two-component chiral p-wave superconductor and normal state in zero external magnetic field. We find a first-order phase transition from the normal state to a chiral superconducting state, due to interplay between vortices and domain walls.

  • 122.
    Hauschild, Johannes
    et al.
    Tech Univ Munich, Dept Phys, T42,James Franck Str 1, D-85748 Garching, Germany..
    Leviatan, Eyal
    Weizmann Inst Sci, Dept Condensed Matter Phys, IL-7610001 Rehovot, Israel..
    Bardarson, Jens H.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Altman, Ehud
    Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA..
    Zaletel, Michael P.
    Princeton Univ, Dept Phys, Princeton, NJ 08540 USA..
    Pollmann, Frank
    Tech Univ Munich, Dept Phys, T42,James Franck Str 1, D-85748 Garching, Germany..
    Finding purifications with minimal entanglement2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 23, article id 235163Article in journal (Refereed)
    Abstract [en]

    Purification is a tool that allows to represent mixed quantum states as pure states on enlarged Hilbert spaces. A purification of a given state is not unique and its entanglement strongly depends on the particular choice made. Moreover, in one-dimensional systems, the amount of entanglement is linked to how efficiently the purified state can be represented using matrix-product states (MPS). We introduce an MPS based method that allows to find the minimally entangled representation by iteratively minimizing the second Renyi entropy. First, we consider the thermofield double purification and show that its entanglement can be strongly reduced especially at low temperatures. Second, we show that a slowdown of the entanglement growth following a quench of an infinite temperature state is possible.

  • 123.
    Hellsvik, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory. KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Thonig, Danny
    Modin, Klas
    Iusan, Diana
    Bergman, Anders
    Eriksson, Olle
    Bergqvist, Lars
    Delin, Anna
    General method for atomistic spin-lattice dynamics with first-principles accuracy2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 10, article id 104302Article in journal (Refereed)
    Abstract [en]

    We present a computationally efficient and general first-principles based method for spin-lattice simulations for solids and clusters. The method is based on a coupling of atomistic spin dynamics and molecular dynamics simulations, expressed through a spin-lattice Hamiltonian, where the bilinear magnetic term is expanded up to second order in displacement. The effect of first-order spin-lattice coupling on the magnon and phonon dispersion in bcc Fe is reported as an example, and we observe good agreement with previous simulations. We also illustrate the coupled spin-lattice dynamics method on a more conceptual level, by exploring dissipation-free spin and lattice motion of small magnetic clusters (a dimer, trimer, and tetramer). The method discussed here opens the door for a quantitative description and understanding of the microscopic origin of many fundamental phenomena of contemporary interest, such as ultrafast demagnetization, magnetocalorics, and spincaloritronics.

  • 124.
    Herviou, Loic
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Bardarson, Jens H.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    L-2 localization landscape for highly excited states2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 22, article id 220201Article in journal (Refereed)
    Abstract [en]

    The localization landscape [M. Filoche and S. Mayboroda, Proc. Natl. Acad. Sci. USA 109, 14761 (2012)] gives direct access to the localization of bottom-of-band eigenstates in noninteracting disordered systems. We generalize this approach to eigenstates at arbitrary energies in systems with or without internal degrees of freedom by introducing a modified L-2 landscape, and we demonstrate its accuracy in a variety of archetypal models of Anderson localization in one and two dimensions. This L-2-landscape function can be efficiently computed using hierarchical methods that allow evaluating the diagonal of a well-chosen Green's function. We compare our approach to other landscape methods, bringing insights on their strengths and limitations. Our approach is general and can in principle be applied to both studies of topological Anderson transitions and many-body localization.

  • 125.
    Herviou, Loic
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Bardarson, Jens H.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Regnault, Nicolas
    Princeton Univ, Joseph Henry Labs, Princeton, NJ 08544 USA.;Princeton Univ, Dept Phys, Princeton, NJ 08544 USA.;Univ Paris Diderot, Univ PSL, Sorbonne Univ, Lab Phys,Ecole Normale Super,ENS,CNRS,Sorbonne Pa, Paris, France..
    Many-body localization in a fragmented Hilbert space2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, no 13, article id 134207Article in journal (Refereed)
    Abstract [en]

    We study many-body localization (MBL) in a pair-hopping model exhibiting strong fragmentation of the Hilbert space. We show that several Krylov subspaces have both ergodic statistics in the thermodynamic limit and a dimension that scales much slower than the full Hilbert space but still exponentially. Such a property allows us to study the MBL phase transition in systems including up to 64 spins. The different Krylov spaces that we consider show clear signatures of a many-body localization transition, both in the Kullback-Leibler divergence of the distribution of their level spacing ratio and their entanglement properties. However, they also present distinct scalings with the system size. Depending on the subspace, the critical disorder strength can be nearly independent of the system size or conversely show an approximately linear increase with the number of spins.

  • 126.
    Herviou, Loic
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Bera, Soumya
    Bardarson, Jens H.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Multiscale entanglement clusters at the many-body localization phase transition2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 13, article id 134205Article in journal (Refereed)
    Abstract [en]

    We numerically study the formation of entanglement clusters across the many-body localization transition. We observe a crossover from strong many-body entanglement in the ergodic phase to weak local correlations in the localized phase, with continuous clusters throughout the phase diagram. Critical states close to the transition have a structure compatible with fractal or multiscale-entangled states, characterized by entanglement at multiple levels: small strongly entangled clusters are weakly entangled together to form larger clusters. The critical point therefore features subthermal entanglement and a power-law distributed cluster size. Upon entering the localized phase, the power-law distribution seems to persist with a varying power that crosses over into a stretched exponent before eventually becoming exponential deep in the localized phase. These results are in agreement with some of the recently proposed phenomenological renormalization-group schemes characterizing the many-body localized critical point, and serve to constrain other such schemes.

  • 127.
    Herviou, Loic
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Le Hur, Karyn
    Univ Paris Saclay, Ctr Phys Theor, CNRS, Ecole Polytech, F-91128 Palaiseau, France..
    Mora, Christophe
    Univ Paris Diderot, Univ Pierre & Marie Curie, Ecole Normale Super,PSL Res Univ, Lab Pierre Aigrain,Sorbonne Paris Cite,Sorbonne U, 24 Rue Lhomond, F-75231 Paris 05, France..
    Bipartite fluctuations and topology of Dirac and Weyl systems2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 7, article id 075133Article in journal (Refereed)
    Abstract [en]

    Bipartite fluctuations can provide interesting information about entanglement properties and correlations in many-body quantum systems. We address such fluctuations in relation with the topology of Dirac and Weyl quantum systems, in situations where the relevant particle number is not conserved, leading to additional volume laws scaling with the quantum Fisher information. In the case of the p + ip superconductor, we build a relation between charge fluctuations and the associated winding numbers of Dirac cones in the low-energy sector. Topological aspects of the Hamiltonian in the vicinity of these points induce long-range entanglement in real space. We specifically extract analytical expressions for the corner contributions to bipartite fluctuations. We highlight their differences and similarities with the corner functions of the entanglement entropy which characterize the underlying conformal field theory. We provide a detailed analysis of such fluctuation properties, including the role of gap anisotropy, and discuss higher-dimensional Weyl analogs.

  • 128.
    Holmgren, Erik
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Bondarenko, Artem
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. National Academy of Sciences of Ukraine, Ukraine.
    Ivanov, B. A.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Resonant pinning spectroscopy with spin-vortex pairs2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 9, article id 094406Article in journal (Refereed)
    Abstract [en]

    Vortex pairs in magnetic nanopillars with strongly coupled cores and pinning of one of the cores by a morphological defect, are used to perform resonant pinning spectroscopy, in which a microwave excitation applied to the nanopillar produces pinning or depinning of the cores only when the excitation is in resonance with the rotational or gyrational eigenmodes of the specific initial state of the core-core pair. The shift in the eigenmode frequencies between the pinned and depinned states is determined experimentally and explained theoretically, and illustrates the potential for multicore spin-vortex memory with resonant writing of information onto various stable vortex pair states. Further, it is shown how the same resonant spectroscopy techniques applied to a vortex pair can be used as a sensitive nanoscale probe for characterizing morphological defects in magnetic films.

  • 129.
    Hope, Marius K.
    et al.
    Norwegian Univ Sci & Technol, Ctr Quantum Spintron, Dept Phys, NO-7491 Trondheim, Norway..
    Amundsen, Morten
    Nordita SU;Stockholm Univ, SE-10691 Stockholm, Sweden..
    Suri, Dhavala
    MIT, Francis Bitter Magnet Lab, 77 Massachusetts Ave, Cambridge, MA 02139 USA.;MIT, Plasma Sci & Fus Ctr, 77 Massachusetts Ave, Cambridge, MA 02139 USA..
    Moodera, Jagadeesh S.
    MIT, Francis Bitter Magnet Lab, 77 Massachusetts Ave, Cambridge, MA 02139 USA.;MIT, Plasma Sci & Fus Ctr, 77 Massachusetts Ave, Cambridge, MA 02139 USA.;MIT, Dept Phys, 77 Massachusetts Ave, Cambridge, MA 02139 USA..
    Kamra, Akashdeep
    Norwegian Univ Sci & Technol, Ctr Quantum Spintron, Dept Phys, NO-7491 Trondheim, Norway.;Univ Autonoma Madrid, Condensed Matter Phys Ctr IFIMAC, E-28049 Madrid, Spain.;Univ Autonoma Madrid, Dept Fis Teor Mat Condensada, E-28049 Madrid, Spain..
    Interfacial control of vortex-limited critical current in type-II superconductor films2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 18, article id 184512Article in journal (Refereed)
    Abstract [en]

    In a small subset of type-II superconductor films, the critical current is determined by a weakened Bean Livingston barrier posed by the film surfaces to vortex penetration into the sample. A film property thus depends sensitively on the surface or interface to an adjacent material. We theoretically investigate the dependence of vortex barrier and critical current in such films on the Rashba spin-orbit coupling at their interfaces with adjacent materials. Considering an interface with a magnetic insulator, we find the spontaneous supercurrent resulting from the exchange field and interfacial spin-orbit coupling to substantially modify the vortex surface barrier, consistent with a previous prediction. Thus, we show that the critical currents in superconductor-magnet heterostructures can be controlled, and even enhanced, via the interfacial spin-orbit coupling. Since the latter can be controlled via a gate voltage, our analysis predicts a class of heterostructures amenable to gate-voltage modulation of superconducting critical currents. It also sheds light on the recently observed gate-voltage enhancement of critical current in NbN films.

  • 130.
    Hårdensson Berntsen, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Götberg, Olof
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Tjernberg, Oscar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Reinvestigation of the giant Rashba-split states on Bi-covered Si(111)2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 12, article id 125148Article in journal (Refereed)
    Abstract [en]

    We study the electronic and spin structures of the giant Rashba-split surface states of the Bi/Si(111)-(root 3 x root 3)R30 degrees trimer phase by means of spin- and angle-resolved photoelectron spectroscopy (spin-ARPES). Supported by tight-binding calculations of the surface state dispersion and spin orientation, our findings show that the spin experiences a vortexlike structure around the (Gamma) over bar point of the surface Brillouin zone-in accordance with the standard Rashba model. Moreover, we find no evidence of a spin vortex around the (K) over bar point in the hexagonal Brillouin zone and thus no peculiar Rashba split around this point, something that has been suggested by previous works. Rather the opposite, our results show that the spin structure around (K) over bar can be fully understood by taking into account the symmetry of the Brillouin zone and the intersection of spin vortices centered around the (Gamma) over bar points in neighboring Brillouin zones. As a result, the spin structure is consistently explained within the standard framework of the Rashba model although the spin-polarized surface states experience a more complex dispersion compared to free-electron-like parabolic states.

  • 131.
    Jana, Somnath
    et al.
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden.;Max Born Inst Nichtlineare Opt & Kurzzeitspektrosk, Max Born Str 2A, D-12489 Berlin, Germany..
    Knut, Ronny
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Delczeg-Czirjak, Erna K.
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Malik, Rameez S.
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Stefanuik, Robert
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Terschlusen, Joachim A.
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Chimata, Raghuveer
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Phuyal, Dibya
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Kamalakar, M. Venkata
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Akansel, Serkan
    Uppsala Univ, Dept Engn Sci, Box 534, S-75121 Uppsala, Sweden..
    Primetzhofer, Daniel
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Ahlberg, Martina
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Soderstrom, Johan
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Svedlindh, Peter
    Uppsala Univ, Dept Engn Sci, Box 534, S-75121 Uppsala, Sweden..
    Eriksson, Olle
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Karis, Olof
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Atom-specific magnon-driven ultrafast spin dynamics in Fe1-xNix alloys2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 18, article id L180301Article in journal (Refereed)
    Abstract [en]

    By employing element-specific spectroscopy in the ultrafast time scale in Fe1-xNix alloys, we find a composition-dependent effect in the demagnetization that we relate to electron-magnon scattering and changes in the spin-wave stiffness. In all six measured alloys of different composition, the demagnetization of Ni compared to Fe exhibits a delay, an effect which we find is inherent in alloys but not in elemental Fe and Ni. Using a model based on electron-magnon scattering, we extract a spin-wave stiffness from all alloys that show excellent agreement with values obtained from other techniques.

  • 132.
    Ji, Shaozheng
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Granas, Oscar
    Uppsala Univ, Dept Phys & Astron, Mat Theory, S-75120 Uppsala, Sweden..
    Rossnagel, Kai
    Christian Albrechts Univ Kiel, Inst Expt & Angew Phys, D-24098 Kiel, Germany.;DESY, Ruprecht Haensel Lab, D-22607 Hamburg, Germany..
    Weissenrieder, Jonas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. KTH Royal Inst Technol, Sch Engn Sci, Mat & Nano Phys, SE-10044 Stockholm, Sweden..
    Transient three-dimensional structural dynamics in 1T -TaSe22020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 9, article id 094303Article in journal (Refereed)
    Abstract [en]

    We report on thermal and optically driven transitions between the commensurate (C) and incommensurate (IC) charge-density wave (CDW) phases of 1T−TaSe2. Optical excitation results in suppression of the C-CDW on a subpicosecond timescale. The optically driven C to IC transition involves a short-lived (∼1 ps) unreconstructed phase. Nucleation of an IC phase stacking order is observed already at ∼4 ps following photoexcitation. The short timescales involved in establishing the stacking order implies that the nucleation of the IC phase is influenced by the local geometry of the adjacent layers such that the stacking direction of the C phase determines the stacking direction of the IC phase. From this follows that the nucleation of the IC-CDW is inherently three dimensional (3D). We observe the activation of a coherent shear mode in the optically driven transitions to the transiently stabilized unreconstructed phase. The activation mechanism starts with a rapid lifting of the periodic lattice distortions (PLD) of the Ta sublattice which results in formation of local transient velocity disparities in the Se sublattice. The local differences in Se-phonon amplitudes result in noncompensated shear forces between the layers. This is an example of a multistep coherent launching mechanism. The energy of the optically excited electronic state dissipates energy into modes of the PLD through strong electron-phonon coupling. The rapid suppression of the PLD launches the third step, a coherent vibrational shear mode with low dissipation. The results highlight the importance in considering the 3D nature of the CDWs in the analysis of both structure and dynamics in transition-metal dichalcogenides.

  • 133. Jukimenko, O.
    et al.
    Modestov, Mikhail
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ.
    Dion, C. M.
    Marklund, M.
    Bychkov, V.
    Multilevel model for magnetic deflagration in nanomagnet crystals2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 17, article id 174403Article in journal (Refereed)
    Abstract [en]

    We extend the existing theoretical model for determining the characteristic features of magnetic deflagration in nanomagnet crystals. For the first time, all energy levels are accounted for calculation of the the Zeeman energy, the deflagration velocity, and other parameters. It reduces the final temperature and significantly changes the propagation velocity of the spin-flipping front. We also consider the effect of a strong transverse magnetic field, and show that the latter significantly modifies the spin-state structure, leading to an uncertainty concerning the activation energy of the spin flipping. Our front velocity prediction for a crystal of Mn-12 acetate in a longitudinal magnetic field is in much better agreement with experimental data than the previous reduced-model results.

  • 134.
    Juricic, Vladimir
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Abergel, David S. L.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    First-order quantum phase transition in three-dimensional topological band insulators2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 16, article id 161403Article in journal (Refereed)
    Abstract [en]

    Topological states of matter are characterized by global topological invariants which change their value across a topological quantum phase transition. It is commonly assumed that the transition between topologically distinct noninteracting gapped phases of fermions is necessarily accompanied by the closing of the band gap as long as the symmetries of the system are maintained. We show that such a quantum phase transition is possible without closing the gap in the case of a three-dimensional topological band insulator. We demonstrate this by calculating the free energy of the minimal model for a topological insulator, the Bernevig-Hughes-Zhang model, and show that as the band curvature continuously varies, a jump between the band-gap minima corresponding to the topologically trivial and nontrivial insulators occurs. Therefore, this first-order phase transition is a generic feature of three-dimensional topological band insulators. For a certain parameter range we predict a reentrant topological phase transition. We discuss our findings in connection with the recent experimental observation of a discontinuous topological phase transition in a family of topological crystalline insulators.

  • 135.
    Jöns, Klaus D.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics. AlbaNova University Center.
    Stensson, Katarina
    KTH, School of Engineering Sciences (SCI), Applied Physics. AlbaNova University Center.
    Reindl, Marcus
    Swillo, Marcin
    KTH, School of Engineering Sciences (SCI), Applied Physics. AlbaNova University Center.
    Huo, Yongheng
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics. AlbaNova University Center.
    Rastelli, Armando
    Trotta, Rinaldo
    Björk, Gunnar
    KTH, School of Engineering Sciences (SCI), Applied Physics. AlbaNova University Center.
    Two-photon interference from two blinking quantum emitters2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 7, article id 075430Article in journal (Refereed)
    Abstract [en]

    We investigate the effect of blinking on the two-photon interference measurement from two independent quantum emitters. We find that blinking significantly alters the statistics in the Hong-Ou-Mandel second-order intensity correlation function g((2))(tau) and the outcome of two-photon interference measurements performed with independent quantum emitters. We theoretically demonstrate that the presence of blinking can be experimentally recognized by a deviation from the g(D)((2))(0) = 0.5 value when distinguishable photons from two emitters impinge on a beam splitter. Our findings explain the significant differences between linear losses and blinking for correlation measurements between independent sources and are experimentally verified using a parametric down-conversion photon-pair source. We show that blinking imposes a mandatory cross-check measurement to correctly estimate the degree of indistinguishability of photons emitted by independent quantum emitters.

  • 136.
    Kaladzhyan, V.
    et al.
    KTH, School of Engineering Sciences (SCI), Physics. Institut de Physique Théorique, Université Paris Saclay, CEA CNRS, Orme des Merisiers, 91190 Gif-sur-Yvette Cedex, France; Laboratoire de Physique des Solides, CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91405 Orsay Cedex, France; Moscow Institute of Physics and Technology, Dolgoprudny 141700, Moscow region, Russia.
    Bena, C.
    Simon, P.
    Topology from triviality2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 10, article id 104512Article in journal (Refereed)
    Abstract [en]

    We show that bringing into proximity two topologically trivial systems can give rise to a topological phase. More specifically, we study a 1D metallic nanowire proximitized by a 2D superconducting substrate with a mixed s-wave and p-wave pairing, and we demonstrate both analytically and numerically that the phase diagram of such a setup can be richer than reported before. Thus apart from the two "expected" well-known phases (i.e., where the substrate and the wire are both simultaneously trivial or topological), we show that there exist two peculiar phases in which the nanowire can be in a topological regime while the substrate is trivial and vice versa. 

  • 137.
    Kaladzhyan, V
    et al.
    KTH, School of Engineering Sciences (SCI), Physics. Univ Paris Sud, Univ Paris Saclay, Lab Phys Solides, CNRS, F-91405 Orsay, France..
    Zyuzin, A. A.
    Aalto Univ, Dept Appl Phys LTL, POB 15100, FI-00076 Aalto, Finland.;Ioffe Phys Tech Inst, St Petersburg 194021, Russia..
    Simon, P.
    Univ Paris Sud, Univ Paris Saclay, Lab Phys Solides, CNRS, F-91405 Orsay, France..
    RKKY interaction on the surface of three-dimensional Dirac semimetals2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 16, article id 165302Article in journal (Refereed)
    Abstract [en]

    We study the RKKY interaction between two magnetic impurities located on the surface of a three-dimensional Dirac semimetal with two Dirac nodes in the band structure. By taking into account both bulk and surface contributions to the exchange interaction between the localized spins, we demonstrate that the surface contribution in general dominates the bulk one at distances larger than the inverse node separation due to a weaker power-law decay. We find a strong anisotropy of the surface term with respect to the spins being aligned along the node separation axis or perpendicular to it. In the many impurity dilute regime, this implies formation of quasi-one-dimensional magnetic stripes orthogonal to the node axis. We also discuss the effects of a surface spin-mixing term coupling electrons from spin-degenerate Fermi arcs.

  • 138.
    Kaladzhyan, Vardan
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Bardarson, Jens H.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Quantized Fermi arc mediated transport in Weyl semimetal nanowires2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 8, article id 085424Article in journal (Refereed)
    Abstract [en]

    We study longitudinal transport in Weyl semimetal nanowires, both in the absence and in the presence of a magnetic flux threading the nanowires. We identify two qualitatively different regimes of transport with respect to the chemical potential in the nanowires. In the "surface regime," for low doping, most of the conductance occurs through the Fermi arc surface states, and it rises in steps of one quantum of conductance as a function of the chemical potential; furthermore, with varying flux the conductance changes in steps of one quantum of conductance with characteristic Fabry-Perot interference oscillations. In the "bulk-surface regime," for highly doped samples, the dominant contribution to the conductance is quadratic in the chemical potential, and mostly conditioned by the bulk states; the flux dependence shows clearly that both the surface and the bulk states contribute. The two aforementioned regimes prove that the contribution of Fermi arc surface states is salient and, therefore, crucial for understanding transport properties of finite-size Weyl semimetal systems. Last but not least, we demonstrate that both regimes are robust to disorder.

  • 139.
    Kaladzhyan, Vardan
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Bena, Cristina
    Univ Paris Saclay, Inst Phys Theor, CEA CNRS, F-91190 Gif Sur Yvette, France..
    Obtaining Majorana and other boundary modes from the metamorphosis of impurity-induced states: Exact solutions via the T-matrix2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 8, article id 081106Article in journal (Refereed)
    Abstract [en]

    We provide here a direct and exact formalism to describe the formation of edge or surface states, as well as to calculate boundary Green's functions. Modeling the boundary as an impurity potential, we show via the T-matrix formalism that the impurity states evolve into boundary modes when the impurity potential goes to infinity. We apply this technique to obtain Majorana states in one- (1D) and two-dimensional Kitaev systems. For the 1D case we also calculate the corresponding boundary Green's functions. We argue that our formalism can be applied to other topological models, as well as to any model exhibiting edge states.

  • 140.
    Kanasugi, Shota
    et al.
    Kyoto Univ, Dept Phys, Kyoto 6068502, Japan..
    Kuzmanovski, Dushko
    KTH Royal Inst Technol, NORDITA, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden.;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.;Univ Connecticut, Dept Phys, Storrs, CT 06269 USA..
    Yanase, Youichi
    Kyoto Univ, Dept Phys, Kyoto 6068502, Japan.;Inst Mol Sci, Okazaki, Aichi 4448585, Japan..
    Ferroelectricity-induced multiorbital odd-frequency superconductivity in SrTiO32020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, no 18, article id 184506Article in journal (Refereed)
    Abstract [en]

    We demonstrate that SrTiO3 can be a platform for observing the bulk odd-frequency superconducting state owing to its multiorbital/multiband nature. We consider a three-orbital tight-binding model for SrTiO3 in the vicinity of a ferroelectric critical point. Assuming an intraorbital spin-singlet s-wave superconducting order parameter, it is shown that the odd-frequency pair correlations are generated due to the intrinsic LS coupling which leads to local orbital mixing. Furthermore, we show the existence of additional odd-frequency pair correlations in the ferroelectric phase, which is induced by an odd-parity orbital hybridization term proportional to the ferroelectric order parameter. We also perform a group theoretical classification of the odd-frequency pair amplitudes based on the fermionic and space group symmetries of the system. The classification table enables us to predict the dominant components of the odd-frequency pair correlations based on the symmetry of the normal state Hamiltonian that we take into account. Furthermore, we show that experimental signatures of odd-parity orbital hybridization, which is an essential ingredient for ferroelectricity-induced odd-frequency pair correlations, can be observed in the spectral functions and density of states.

  • 141.
    Kapran, O. M.
    et al.
    Stockholm Univ, Alballova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden..
    Golod, T.
    Stockholm Univ, Alballova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden..
    Iovan, Adrian
    KTH, School of Engineering Sciences (SCI), Applied Physics. Stockholm Univ, Alballova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden..
    Sidorenko, A. S.
    Inst Elect Engn & Nanotechnol ASM, MD-2028 Kishinev, Moldova.;IS Turgenev Orel State Univ, Oryol 302026, Russia..
    Golubov, A. A.
    Univ Twente, Fac Sci & Technol, NL-7500 AE Enschede, Netherlands.;Univ Twente, MESA Inst Nanotechnol, NL-7500 AE Enschede, Netherlands.;State Univ, Moscow Inst Phys & Technol, Dolgoprudnyi 141700, Russia..
    Krasnov, V. M.
    Stockholm Univ, Alballova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden.;State Univ, Moscow Inst Phys & Technol, Dolgoprudnyi 141700, Russia..
    Crossover between short- and long-range proximity effects in superconductor/ferromagnet/superconductor junctions with Ni-based ferromagnets2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, no 9, article id 094509Article in journal (Refereed)
    Abstract [en]

    We study superconductor/ferromagnet/superconductor junctions with CuNi, PtNi, or Ni interlayers. Remarkably, we observe that supercurrents through Ni can be significantly larger than through diluted alloys. The phenomenon is attributed to the dirtiness of disordered alloys leading to a short coherence length despite a small exchange energy. To the contrary, pure Ni is clean resulting in a coherence length as long as in a normal metal. Analysis of temperature dependencies of critical currents reveals a crossover from short (dirty) to long (clean) range proximity effects in Pt1-xNix with increasing Ni concentration. Our results point out that structural properties of a ferromagnet play a crucial role for the proximity effect and indicate that conventional strong-but-clean ferromagnets can be advantageously used in superconducting spintronic devices.

  • 142.
    Karmakar, Debjani
    et al.
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden; Technical Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
    Pereiro, Manuel
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden.
    Hasan, Md Nur
    Department of Chemical and Biological Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector-III, SaltLake, Kolkata 700 106, India.
    Bharati, Ritadip
    School of Physical Sciences, National Institute of Science Education and Research, Homi Bhabha National Institute (HBNI), Jatni, 752050 Odisha, India.
    Hellsvik, Johan
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory. KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for High Performance Computing, PDC.
    Delin, Anna
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Pal, Samir Kumar
    Department of Chemical and Biological Sciences, S. N. Bose National Centre for Basic Sciences, Block JD, Sector-III, SaltLake, Kolkata 700 106, India.
    Bergman, Anders
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden.
    Sharma, Shivalika
    Asia Pacific Center for Theoretical Physics, Pohang 37673, Republic of Korea.
    Di Marco, Igor
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden; Asia Pacific Center for Theoretical Physics, Pohang 37673, Republic of Korea; Department of Physics, Pohang University of Science and Technology, Pohang 37673, Republic of Korea.
    Thunström, Patrik
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden.
    Oppeneer, Peter M.
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden.
    Eriksson, Olle
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden.
    Magnetism in A V3Sb5 (A=Cs, Rb, K): Complex landscape of dynamical magnetic textures2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, no 17, article id 174413Article in journal (Refereed)
    Abstract [en]

    We have investigated the dynamical magnetic properties of the V-based kagome stibnite compounds by combining the ab initio-extracted magnetic parameters of a spin-Hamiltonian, like inter-site exchange parameters, magnetocrystalline anisotropy and site projected magnetic moments, with full-fledged simulations of atomistic spin- dynamics. Our calculations reveal that, in addition to a ferromagnetic order along the [001] direction, the system hosts a complex landscape of magnetic configurations comprised of commensurate and incommensurate spin spirals along the [010] direction. The presence of such chiral magnetic textures may be the key toward solving the mystery about the origin of the experimentally observed inherent breaking of the C6 rotational, mirror, and the time-reversal symmetry.

  • 143. Keatley, P. S.
    et al.
    Sani, Sohrab Redjai
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Hrkac, G.
    Mohseni, S. M.
    Durrenfeld, P.
    Akerman, J.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Hicken, R. J.
    Superharmonic injection locking of nanocontact spin-torque vortex oscillators2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 9, article id 094404Article in journal (Refereed)
    Abstract [en]

    Superharmonic injection locking of single nanocontact (NC) spin-torque vortex oscillators (STVOs) subject to a small microwave current has been explored. Frequency locking was observed up to the fourth harmonic of the STVO fundamental frequency f(0) in microwave magnetoelectronic measurements. The large frequency tunability of the STVO with respect to f(0) allowed the device to be locked to multiple subharmonics of the microwave frequency f(RF), or to the same subharmonic over a wide range of fRF by tuning the dc current. In general, analysis of the locking range, linewidth, and amplitude showed that the locking efficiency decreased as the harmonic number increased, as expected for harmonic synchronization of a nonlinear oscillator. Time-resolved scanning Kerr microscopy (TRSKM) revealed significant differences in the spatial character of the magnetization dynamics of states locked to the fundamental and harmonic frequencies, suggesting significant differences in the vortex core trajectories within the same device. Superharmonic injection locking of a NC-STVO may open up possibilities for devices such as nanoscale frequency dividers, while differences in the core trajectory may allow mutual synchronization to be achieved in multioscillator networks by tuning the spatial character of the dynamics within shared magnetic layers.

  • 144.
    Khasanov, Rustem
    et al.
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Luetkens, Hubertus
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Morenzoni, Elvezio
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Simutis, Gediminas
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Östlin, Andreas
    Univ Augsburg, Augsburg Ctr Innovat Technol, D-86135 Augsburg, Germany.;Univ Augsburg, Ctr Elect Correlat & Magnetism, Theoret Phys 3, Inst Phys, D-86135 Augsburg, Germany..
    Chioncel, Liviu
    Univ Augsburg, Augsburg Ctr Innovat Technol, D-86135 Augsburg, Germany.;Univ Augsburg, Ctr Elect Correlat & Magnetism, Theoret Phys 3, Inst Phys, D-86135 Augsburg, Germany..
    Amato, Alex
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Superconductivity of Bi-III phase of elemental bismuth: Insights from muon-spin rotation and density functional theory2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 14, article id 140504Article in journal (Refereed)
    Abstract [en]

    Using muon-spin rotation the pressure-induced superconductivity in the Bi-III phase of elemental bismuth (transition temperature T-c similar or equal to 7.05 K) was investigated. A Ginzburg-Landau parameter kappa = lambda/xi = 30(6) (lambda is the magnetic penetration depth, xi is the coherence length) was estimated, which turns out to be the highest among known single element superconductors. The temperature dependence of the superconducting energy gap [Delta(T)] reconstructed from lambda(-2)(T) deviates from the weakly coupled BCS prediction. The coupling strength 2 Delta/k(B)T

  • 145.
    Khasanov, Rustem
    et al.
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Radonjic, Milos M.
    Univ Belgrade, Inst Phys Belgrade, Sci Comp Lab, Ctr Study Complex Syst, Pregrev 118, Belgrade 11080, Serbia..
    Luetkens, Hubertus
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Morenzoni, Elvezio
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Simutis, Gediminas
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Appelt, Wilhelm H.
    Univ Augsburg, Inst Phys, Augsburg Ctr Innovat Technol, Theoret Phys 3, D-86135 Augsburg, Germany.;Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Theoret Phys 3, D-86135 Augsburg, Germany..
    Oestlin, Andreas
    Univ Augsburg, Inst Phys, Augsburg Ctr Innovat Technol, Theoret Phys 3, D-86135 Augsburg, Germany.;Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Theoret Phys 3, D-86135 Augsburg, Germany..
    Chioncel, Liviu
    Univ Augsburg, Inst Phys, Augsburg Ctr Innovat Technol, Theoret Phys 3, D-86135 Augsburg, Germany.;Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Theoret Phys 3, D-86135 Augsburg, Germany..
    Amato, Alex
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Superconducting nature of the Bi-II phase of elemental bismuth2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 17, article id 174506Article in journal (Refereed)
    Abstract [en]

    The superconductivity in the Bi-II phase of elemental bismuth (transition temperature T-c similar or equal to 3.92 K at pressure p similar or equal to 2.80 GPa) was studied experimentally by means of the muon-spin rotation as well as theoretically by using the Eliashberg theory in combination with density functional theory calculations. Experiments reveal that Bi-II is a type-I superconductor with a zero temperature value of the thermodynamic critical field B-c(0) similar or equal to 31.97 mT. The Eliashberg theory approach provides a good agreement with the experimental T-c and the temperature evolution of B-c . The estimated value for the retardation (coupling) parameter k(B)T(c)/omega(In) approximate to 0.07 (omega(In) is the logarithmically averaged phonon frequency) suggests that Bi-II is an intermediately coupled superconductor.

  • 146.
    Kholtobina, Anastasiia S.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Forslund, Axel
    Univ Stuttgart, Inst Mat Sci, D-70569 Stuttgart, Germany..
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures. Mat Ctr Leoben Forsch GmbH, Roseggerstr 12, A-8700 Leoben, Austria..
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala Univ, Dept Phys & Astron, Div Mat Theory, S-75120 Uppsala, Sweden..
    Skorodumova, Natalia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures.
    Temperature dependence of (111) and (110) ceria surface energy2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 3, article id 035407Article in journal (Refereed)
    Abstract [en]

    High-temperature properties of ceria surfaces are important for many applications. Here, we report the temperature dependencies of surface energy for (111) and (110) CeO2 obtained in the framework of the extended two-stage up-sampled thermodynamic integration using Langevin dynamics. The method was used together with machine-learning potentials called moment tensor potentials (MTPs), which were fitted to the results of the ab initio molecular dynamics calculations for (111) and (110) CeO2 at different temperatures. The parameters of MTP training and fitting were tested, and the optimal algorithm for the ceria systems was proposed. We found that the temperature increases from 0 to 2100 K led to the decrease of the Helmholtz free energy of (111) CeO2 from 0.78 to 0.64 J/m2. The energy of (110) CeO2 dropped from 1.19 J/m2 at 0 K to 0.92 J/m2 at 1800 K. We show that it is important to consider anharmonicity, as simple consideration of volume expansion gives the wrong temperature dependencies of the surface energies.

  • 147.
    Klarbring, Johan
    et al.
    Linkoping Univ, Dept Phys Chem & Biol IFM, SE-58183 Linkoping, Sweden..
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden.
    Simak, Sergei I.
    Linkoping Univ, Dept Phys Chem & Biol IFM, SE-58183 Linkoping, Sweden..
    Finite-temperature lattice dynamics and superionic transition in ceria from first principles2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 10, article id 104309Article in journal (Refereed)
    Abstract [en]

    Ab initio molecular dynamics (AIMD) in combination with the temperature dependent effective potential (TDEP) method has been used to go beyond the quasiharmonic approximation and study the lattice dynamics in ceria, CeO2, at finite temperature. The results indicate that the previously proposed connection between the B-1u phonon mode turning imaginary and the transition to the superionic phase in fluorite structured materials is an artifact of the failure of the quasiharmonic approximation in describing the lattice dynamics at elevated temperatures. We instead show that, in the TDEP picture, a phonon mode coupling to the E-u mode prevents the B-1u mode from becoming imaginary. We directly observe the superionic transition at high temperatures in our AIMD simulations and find that it is initiated by the formation of oxygen Frenkel pairs (FP). These FP are found to form in a collective process involving simultaneous motion of two oxygen ions.

  • 148. Klyushina, E. S.
    et al.
    Lake, B.
    Islam, A. T. M. N.
    Park, J. T.
    Schneidewind, A.
    Guidi, T.
    Goremychkin, E. A.
    Klemke, B.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Investigation of the spin-1 honeycomb antiferromagnet BaNi2V2O8 with easy-plane anisotropy2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 21, article id 214428Article in journal (Refereed)
    Abstract [en]

    The magnetic properties of the two-dimensional, S = 1 honeycomb antiferromagnet BaNi2V2O8 have been comprehensively studied using dc susceptibility measurements and inelastic neutron scattering techniques. The magnetic excitation spectrum is found to be dispersionless within experimental resolution between the honeycomb layers, while it disperses strongly within the honeycomb plane where it consists of two gapped spin-wave modes. The magnetic excitations are compared to linear spin-wave theory allowing the Hamiltonian to be determined. The first-and second-neighbor magnetic exchange interactions are antiferromagnetic and lie within the ranges 10.90 meV <= J(n) <= 13.35 meV and 0.85 meV <= J(nn) <= 1.65 meV, respectively. The interplane coupling J(out) is four orders of magnitude weaker than the intraplane interactions, confirming the highly two-dimensional magnetic behavior of this compound. The sizes of the energy gaps are used to extract the magnetic anisotropies and reveal substantial easy-plane anisotropy and a very weak in-plane easy-axis anisotropy. Together these results reveal that BaNi2V2O8 is a candidate compound for the investigation of vortex excitations and Berezinsky-Kosterliz-Thouless phenomenon.

  • 149.
    Klyushina, E. S.
    et al.
    Helmholtz Zentrum Berlin Mat & Energie, D-14109 Berlin, Germany.;Tech Univ Berlin, Inst Festkorperphys, D-10623 Berlin, Germany..
    Reuther, J.
    Helmholtz Zentrum Berlin Mat & Energie, D-14109 Berlin, Germany.;Free Univ Berlin, Dahlem Ctr Complex Quantum Syst, Arnimallee 14, D-14195 Berlin, Germany.;Free Univ Berlin, Inst Theoret Phys, Arnimallee 14, D-14195 Berlin, Germany..
    Weber, L.
    Rhein Westfal TH Aachen, Inst Theoret Solid State Phys, JARA FIT, D-52056 Aachen, Germany.;Rhein Westfal TH Aachen, JARA HPC, D-52056 Aachen, Germany..
    Islam, A. T. M. N.
    Helmholtz Zentrum Berlin Mat & Energie, D-14109 Berlin, Germany..
    Lord, J. S.
    STFC Rutherford Appleton Lab, ISIS Facil, Didcot OX11 0QX, Oxon, England..
    Klemke, B.
    Helmholtz Zentrum Berlin Mat & Energie, D-14109 Berlin, Germany..
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Wessel, S.
    Rhein Westfal TH Aachen, Inst Theoret Solid State Phys, JARA FIT, D-52056 Aachen, Germany.;Rhein Westfal TH Aachen, JARA HPC, D-52056 Aachen, Germany..
    Lake, B.
    Helmholtz Zentrum Berlin Mat & Energie, D-14109 Berlin, Germany.;Tech Univ Berlin, Inst Festkorperphys, D-10623 Berlin, Germany..
    Signatures for Berezinskii-Kosterlitz-Thouless critical behavior in the planar antiferromagnet BaNi2V2O82021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 6, article id 064402Article in journal (Refereed)
    Abstract [en]

    We investigate the critical properties of the spin-1 honeycomb antiferromagnet BaNi2V2O8, both below and above the ordering temperature T-N using neutron diffraction and muon spin rotation measurements. Our results characterize BaNi2V2O8 as a two-dimensional (2D) antiferromagnet across the entire temperature range, displaying a series of crossovers from 2D XY to 2D XXZ and then to 2D Heisenberg behavior with increasing temperature. In particular, the extracted critical exponent of the order parameter reveals a narrow temperature regime close to T-N, in which the system behaves as a 2D XY antiferromagnet. Above T-N, evidence for Berezinskii-Kosterlitz-Thouless behavior driven by vortex excitations is obtained from the scaling of the correlation length. Our experimental results are in agreement with classical and quantum Monte Carlo simulations performed using microscopic magnetic model Hamiltonians for BaNi2V2O8.

  • 150.
    Kochergin, Daniil
    et al.
    Moscow Institute of Physics and Technology, Dolgoprudny 141700, Russia; Laboratory of Complex Networks, Center for Neurophysics and Neuromorphic Technologies, Moscow 119991, Russia.
    Khaymovich, Ivan M.
    Nordita SU; Institute for Physics of Microstructures, Russian Academy of Sciences, 603950 Nizhny Novgorod, GSP-105, Russia.
    Valba, Olga
    Laboratory of Complex Networks, Center for Neurophysics and Neuromorphic Technologies, Moscow 119991, Russia; Higher School of Economics, Moscow 123458, Russia.
    Gorsky, Alexander
    Laboratory of Complex Networks, Center for Neurophysics and Neuromorphic Technologies, Moscow 119991, Russia; Institute for Information Transmission Problems, Moscow 127994, Russia.
    Anatomy of the fragmented Hilbert space: Eigenvalue tunneling, quantum scars, and localization in the perturbed random regular graph2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, no 9, article id 094203Article in journal (Refereed)
    Abstract [en]

    We consider the properties of the random regular graph with node degree d perturbed by chemical potentials μk for a number of short k-cycles. We analyze both numerically and analytically the phase diagram of the model in the (μk,d) plane. The critical curve separating the homogeneous and clusterized phases is found and it is demonstrated that the clusterized phase itself generically is separated as the function of d into the phase with ideal clusters and phase with coupled ones when the continuous spectrum gets formed. The eigenstate spatial structure of the model is investigated and it is found that there are localized scarlike states in the delocalized part of the spectrum, that are related to the topologically equivalent nodes in the graph. We also reconsider the localization of the states in the nonperturbative band formed by eigenvalue instantons and find the semi-Poisson level spacing distribution. The Anderson transition for the case of combined (k-cycle) structural and diagonal (Anderson) disorders is investigated. It is found that the critical diagonal disorder gets reduced sharply at the clusterization phase transition but does it unevenly in nonperturbative and mid-spectrum bands, due to the scars, present in the latter. The applications of our findings to 2d quantum gravity are discussed.

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