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  • 1.
    Ahmed, Aamna
    et al.
    Indian Inst Sci Educ & Res, Dept Phys, Bhopal 462066, Madhya Pradesh, India..
    Ramachandran, Ajith
    Christ Coll, Dept Phys, Irinjalakuda 680125, Kerala, India..
    Khaymovich, Ivan
    Nordita SU; Stockholm Univ, Hannes Alfvens Vag 12, SE-10691 Stockholm, Sweden.
    Sharma, Auditya
    Indian Inst Sci Educ & Res, Dept Phys, Bhopal 462066, Madhya Pradesh, India..
    Flat band based multifractality in the all-band-flat diamond chain2022Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, nr 20, artikel-id 205119Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the effect of quasiperiodic Aubry-Andre disorder on the energy spectrum and eigenstates of a one-dimensional all-band-flat (ABF) diamond chain. The ABF diamond chain possesses three dispersionless flat bands with all the eigenstates compactly localized on two unit cells in the zero disorder limit. The fate of the compact localized states in the presence of the disorder depends on the symmetry of the applied potential. We consider two cases here: a symmetric one, where the same disorder is applied to the top and bottom sites of a unit cell and an antisymmetric one, where the disorder applied to the top and bottom sites are of equal magnitude but with opposite signs. Remarkably, the symmetrically perturbed lattice preserves compact localization, although the degeneracy is lifted. When the lattice is perturbed antisymmetrically, not only is the degeneracy is lifted but compact localization is also destroyed. Fascinatingly, all eigenstates exhibit a multifractal nature below a critical strength of the applied potential. A central band of eigenstates continue to display an extended yet nonergodic behavior for arbitrarily large strengths of the potential. All other eigenstates exhibit the familiar Anderson localization above the critical potential strength. We show how the antisymmetric disordered model can be mapped to a pi /4 rotated square lattice with the nearest and selective next-nearest-neighbor hopping and a staggered magnetic field-such models have been shown to exhibit multifractality. Surprisingly, the antisymmetric disorder (with an even number of unit cells) preserves chiral symmetry-we show this by explicitly writing down the chiral operator.

  • 2.
    Aksoy, Omer M.
    et al.
    Paul Scherrer Inst, Condensed Matter Theory Grp, CH-5232 Villigen, Switzerland..
    Chandrasekaran, Anirudh
    Loughborough Univ, Dept Phys, Loughborough LE11 3TU, England..
    Tiwari, Apoorv
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Neupert, Titus
    Univ Zurich, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Chamon, Claudio
    Boston Univ, Dept Phys, Boston, MA 02215 USA..
    Mudry, Christopher
    Paul Scherrer Inst, Condensed Matter Theory Grp, CH-5232 Villigen, Switzerland.;EPF Lausanne, Inst Phys, CH-1015 Lausanne, Switzerland..
    Single monkey-saddle singularity of a Fermi surface and its instabilities2023Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, nr 20, artikel-id 205129Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fermi surfaces can undergo sharp transitions under smooth changes of parameters. Such transitions can have a topological character, as is the case when a higher-order singularity, one that requires cubic or higher-order terms to describe the electronic dispersion near the singularity, develops at the transition. When time-reversal and inversion symmetries are present, odd singularities can only appear in pairs within the Brillouin zone. In this case, the combination of the enhanced density of states that accompanies these singularities and the nesting between the pairs of singularities leads to interaction-driven instabilities. We present examples of single n = 3 (monkeysaddle) singularities when time-reversal and inversion symmetries are broken. We then turn to the question of what instabilities are possible when the singularities are isolated. For spinful electrons, we find that the inclusion of repulsive interactions destroys any isolated monkey-saddle singularity present in the noninteracting spectrum by developing Stoner or Lifshitz instabilities. In contrast, for spinless electrons and at the mean-field level, we show that an isolated monkey-saddle singularity can be stabilized in the presence of short-range repulsive interactions.

  • 3. Alidoust, M.
    et al.
    Halterman, K.
    Zyuzin, A. A.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Superconductivity in type-II Weyl semimetals2017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, nr 15, artikel-id 155124Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study superconductivity in a Weyl semimetal with a tilted dispersion around two Weyl points of opposite chirality. In the absence of any tilt, the state with zero momentum pairing between two Fermi sheets enclosing each Weyl point has four point nodes in the superconducting gap function. Moreover, the surface of the superconductor hosts Fermi arc states and Majorana flat bands. We show that a quantum phase transition occurs at a critical value of the tilt, at which two gap nodes disappear by merging at the center of the first Brillouin zone, or by escaping at its edges, depending on the direction of the tilt. The region in the momentum space that the Majorana flat band occupies is found to increase as the tilt parameter is made larger. Additionally, the superconducting critical temperature and electronic specific heat can be enhanced in the vicinity of the quantum phase transition due to the singularity in the electronic density of states.

  • 4. Alidoust, Mohammad
    et al.
    Zyuzin, Alexander
    KTH, Skolan för teknikvetenskap (SCI), Teoretisk fysik.
    Halterman, Klaus
    Pure odd-frequency superconductivity at the cores of proximity vortices2017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, nr 4, artikel-id 045115Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    After more than a decade, direct observation of the odd frequency triplet pairing state in superconducting hybrid structures remains elusive. We propose an experimentally feasible setup that can unambiguously reveal the zero energy peak due to proximity-induced equal spin superconducting triplet correlations. We theoretically investigate a two-dimensional Josephson junction in the diffusive regime. The nanostructure consists of a normal metal sandwiched between two ferromagnetic layers with spiral magnetization patterns. By applying an external magnetic field perpendicular to the junction plane, vortices nucleate in the normal metal. The calculated energy and spatially resolved density of states, along with the pair potential, reveal that remarkably, only triplet Cooper pairs survive in the vortex cores. These isolated odd frequency triplet correlations result in well defined zero energy peaks in the local density of states that can be identified through tunneling spectroscopy experiments. Moreover, the diffusive regime considered here rules out the possibility of Andreev bound states in the vortex core as contributors to the zero energy peaks.

  • 5.
    Amundsen, Morten
    et al.
    Nordita SU.
    V. Bobkova, Irina
    Inst Solid State Phys, Chernogolovka, Moscow 142432, Russia.;Moscow Inst Phys & Technol, Dolgoprudny, Moscow 141700, Russia.;Natl Res Univ Higher, Sch Econ, Moscow 101000, Russia..
    Kamra, Akashdeep
    Univ Autonoma Madrid, Dept Fis Teor Mat Condensada, Madrid 28049, Spain.;Condensed Matter Phys Ctr IFIMAC, Madrid 28049, Spain..
    Magnonic spin Joule heating and rectification effects2022Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, nr 14, artikel-id 144411Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Nonlinear devices, such as transistors, enable contemporary computing technologies. We theoretically investigate nonlinear effects, bearing a high fundamental scientific and technical relevance, in magnonics with emphasis on superconductor-ferromagnet hybrids. Accounting for a finite magnon chemical potential, we theoretically demonstrate magnonic spin Joule heating, the spin analog of conventional electronic Joule heating. Besides suggesting a key contribution to magnonic heat transport in a broad range of devices, it provides insights into the thermal physics of nonconserved bosonic excitations. Considering a spin-split superconductor self-consistently, we demonstrate its interface with a ferromagnetic insulator to harbor large tunability of spin and thermal conductances. We further demonstrate hysteretic rectification I-V characteristics in this hybrid, where the hysteresis results from the superconducting state bistability.

  • 6.
    Andrade, Tomas
    et al.
    Univ Barcelona, Inst Ciencies Cosmos, Dept Fis Quant & Astrofis, Marti & Franques 1, E-08028 Barcelona, Spain..
    Krikun, Alexander
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Hannes Alfvens Vag 12, SE-10691 Stockholm, Sweden..
    Thermoelectric transport properties of gapless pinned charge density waves2022Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, nr 4, artikel-id L041118Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Quantum strongly correlated matter exhibits properties which are not easily explainable in the conventional framework of Fermi liquids. Universal effective field theory tools are applicable in these cases regardless of the microscopic details of the quantum system, since they are based on symmetries. It is necessary, however, to construct these effective tools in full generality, avoiding restrictions coming from particular microscopic descriptions which may inadequately constrain the coefficients that enter in the effective theory. In this work we demonstrate with explicit examples how the hydrodynamic coefficients, which have been recently reinstated in the effective theory of pinned charge density waves (CDWs), can affect the phenomenology of the thermoelectric transport in strongly correlated quantum matter. Our examples, based on two classes of holographic models with pinned CDW, have microscopics which are conceptually different from Fermi liquids. Therefore, the above transport coefficients are nonzero, contrary to the conventional approach. We show how these coefficients allow one to take into account the change of sign of the Seebeck coefficient and the low resistivity of the CDW phase of the cuprate high temperature superconductors, without referring to the effects of Fermi surface reconstruction.

  • 7.
    Andresen, Juan Carlos
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Katzgraber, Helmut G.
    Schechter, Moshe
    Random-field-induced disordering mechanism in a disordered ferromagnet: Between the Imry-Ma and the standard disordering mechanism2017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 21, artikel-id 214414Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Random fields disorder Ising ferromagnets by aligning single spins in the direction of the random field in three space dimensions, or by flipping large ferromagnetic domains at dimensions two and below. While the former requires random fields of typical magnitude similar to the interaction strength, the latter Imry-Ma mechanism only requires infinitesimal random fields. Recently, it has been shown that for dilute anisotropic dipolar systems a third mechanism exists, where the ferromagnetic phase is disordered by finite-size glassy domains at a random field of finite magnitude that is considerably smaller than the typical interaction strength. Using large-scale Monte Carlo simulations and zero-temperature numerical approaches, we show that this mechanism applies to disordered ferromagnets with competing short-range ferromagnetic and antiferromagnetic interactions, suggesting its generality in ferromagnetic systems with competing interactions and an underlying spin-glass phase. A finite-size-scaling analysis of the magnetization distribution suggests that the transition might be first order.

  • 8.
    Artiaco, Claudia
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik. Scuola Int Super Studi Avanzati SISSA, Via Bonomea 265, I-34136 Trieste, Italy.;Abdus Salam Int Ctr Theoret Phys, Str Costiera 11, I-34151 Trieste, Italy.;INFN Sez Trieste, Via Valerio 2, I-34127 Trieste, Italy..
    Balducci, Federico
    Scuola Int Super Studi Avanzati SISSA, Via Bonomea 265, I-34136 Trieste, Italy.;Abdus Salam Int Ctr Theoret Phys, Str Costiera 11, I-34151 Trieste, Italy.;INFN Sez Trieste, Via Valerio 2, I-34127 Trieste, Italy..
    Heyl, Markus
    Max Planck Inst Phys Komplexer Syst, Nothnitzer Str 38, D-01187 Dresden, Germany.;Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Theoret Phys 3, D-86135 Augsburg, Germany..
    Russomanno, Angelo
    Max Planck Inst Phys Komplexer Syst, Nothnitzer Str 38, D-01187 Dresden, Germany.;Univ Napoli Federico II, Scuola Super Meridionale, Largo San Marcellino 10, I-80138 Naples, Italy..
    Scardicchio, Antonello
    Abdus Salam Int Ctr Theoret Phys, Str Costiera 11, I-34151 Trieste, Italy.;INFN Sez Trieste, Via Valerio 2, I-34127 Trieste, Italy..
    Spatiotemporal heterogeneity of entanglement in many-body localized systems2022Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, nr 18, artikel-id 184202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a spatiotemporal characterization of the entanglement dynamics in many-body localized (MBL) systems, which exhibits a striking resemblance to dynamical heterogeneity in classical glasses. Specifically, we find that the relaxation times of local entanglement, as measured by the concurrence, are spatially correlated yielding a dynamical length scale for quantum entanglement. As a consequence of this spatiotemporal analysis, we observe that the considered MBL system is made up of dynamically correlated clusters with a size set by this entanglement length scale. The system decomposes into compartments of different activity such as active regions with fast quantum entanglement dynamics and inactive regions where the dynamics is slow. We further find that the relaxation times of the on-site concurrence become broadly distributed and more spatially correlated, as disorder increases or the energy of the initial state decreases. Through this spatiotemporal characterization of entanglement, our work unravels a previously unrecognized connection between the behavior of classical glasses and the genuine quantum dynamics of MBL systems.

  • 9.
    Artiaco, Claudia
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Nava, Andrea
    Univ Calabria, Dipartimento Fis, I-87036 Cosenza, Italy.;Ist Nazl Fis Nucl, Grp collegato Cosenza, I-87036 Cosenza, Italy..
    Fabrizio, Michele
    Scuola Int Super Studi Avanzati SISSA, Via Bonomea 265, I-34136 Trieste, Italy..
    Wetting critical behavior in the quantum Ising model within the framework of Lindblad dissipative dynamics2023Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, nr 10, artikel-id 104201Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the critical behavior, both in space and time, of the wetting interface within the coexistence region around the first-order phase transition of a fully connected quantum Ising model in slab geometry. For that, we employ the Lindblad master equation formalism in which temperature is inherited by the coupling to a dissipative bath, rather than being a functional parameter as in the conventional Cahn's free energy. Lindblad's approach gives not only access to the dissipative dynamics and steady-state configuration of the quantum wetting interface throughout the whole phase diagram but also shows that the wetting critical behavior can be successfully exploited to characterize the phase diagram as an alternative to the direct evaluation of the free energies of the competing phases.

  • 10. Atteia, J.
    et al.
    Bardarson, Jens H.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Cayssol, J.
    Ballistic transport through irradiated graphene2017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 24, artikel-id 245404Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The coherent charge transport through an illuminated graphene ribbon is studied as a function of electronic doping and characteristics of the electromagnetic driving, for monochromatic circularly polarized light. We focus on the DC current carried by 2D bulk carriers which is dominant (over edge transport) for short and wide enough samples. We investigate how the ballistic conductance suppression, due to photon resonances between the valence and conduction bands, evolves when the experimentally tunable parameters are varied. The residual conductance can be associated with evanescent states and related to dynamical gaps in the Floquet quasienergy spectrum.

  • 11.
    Azimi-Mousolou, Vahid
    et al.
    Department of Applied Mathematics and Computer Science, Faculty of Mathematics and Statistics, University of Isfahan, Isfahan 81746-73441, Iran; Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden, Box 516.
    Bergman, Anders
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden, Box 516.
    Delin, Anna
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Eriksson, Olle
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden, Box 516.
    Pereiro, Manuel
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden, Box 516.
    Thonig, Danny
    School of Science and Technology, Örebro University, SE-701 82 Örebro, Sweden.
    Sjöqvist, Erik
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-751 20 Uppsala, Sweden, Box 516.
    Transmon probe for quantum characteristics of magnons in antiferromagnets2023Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, nr 9, artikel-id 094430Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The detection of magnons and their quantum properties, especially in antiferromagnetic (AFM) materials, is a substantial step to realize many ambitious advances in the study of nanomagnetism and the development of energy efficient quantum technologies. The recent development of hybrid systems based on superconducting circuits provides the possibility to engineer quantum sensors that exploit different degrees of freedom. Here, we examine the magnon-photon-transmon hybridization based on bipartite AFM materials, which gives rise to an effective coupling between a transmon qubit and magnons in a bipartite AFM. We demonstrate how magnon modes, their chiralities, and quantum properties, such as nonlocality and two-mode magnon entanglement in bipartite AFMs, can be characterized through the Rabi frequency of the superconducting transmon qubit.

  • 12. Bagschik, Kai
    et al.
    Froemter, Robert
    Bach, Judith
    Beyersdorff, Bjoern
    Mueller, Leonard
    Schleitzer, Stefan
    Berntsen, Magnus H.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. Deutsch Elekt Synchrotron DESY.
    Weier, Christian
    Adam, Roman
    Viefhaus, Jens
    Schneider, Claus Michael
    Gruebel, Gerhard
    Oepen, Hans Peter
    Employing soft x-ray resonant magnetic scattering to study domain sizes and anisotropy in Co/Pd multilayers2016Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, nr 13, artikel-id 134413Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is demonstrated that themagnetic diffraction pattern of the isotropic disorderedmaze pattern is well described utilizing a gamma distribution of domain sizes in a one-dimensional model. From the analysis, the mean domain size and the shape parameter of the distribution are obtained. The model reveals an average domain size that is significantly different from the value that is determined from the peak position of the structure factor in reciprocal space. As a proof of principle, a wedge-shaped (Co-t angstrom/Pd-10 angstrom) 8 multilayer film, that covers the thickness range of the spin-reorientation transition, has been used. By means of soft x-ray resonant magnetic scattering (XRMS) and imaging techniques the thickness-driven evolution of the magnetic properties of the cobalt layers is explored. It is shown that minute changes of the domain pattern concerning domain size and geometry can be investigated and analyzed due to the high sensitivity and lateral resolution of the XRMS technique. The latter allows for the determination of the magnetic anisotropies of the cobalt layers within a thickness range of a few angstroms.

  • 13.
    Balabanov, Oleksandr
    et al.
    Stockholm Univ, AlbaNova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden..
    Ortega-Taberner, Carlos
    Nordita SU.
    Hermanns, Maria
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Department of Physics, Stockholm University, AlbaNova University Center, Stockholm, SE-106 91, Sweden.
    Quantization of topological indices in critical chains at low temperatures2022Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, nr 4, artikel-id 045116Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Various types of topological phenomena at criticality are currently under active research. In this paper we suggest to generalize the known topological quantities to finite temperatures, allowing us to consider gapped and critical (gapless) systems on the same footing. It is then discussed that the quantization of the topological indices, also at critically, is retrieved by taking the low-temperature limit. This idea is explicitly illustrated on a simple case study of chiral critical chains where the quantization is shown analytically and verified numerically. The formalism is also applied for studying robustness of the topological indices to various types of disordering perturbations.

  • 14.
    Balafendiev, Rustam
    et al.
    ITMO Univ, Sch Phys & Engn, St Petersburg 197101, Russia..
    Simovski, Constantin
    Aalto Univ, Sch Elect Engn, Dept Elect & Nanoengn, POB 13000, Aalto 0007, Finland..
    Millar, Alexander J.
    Stockholm Univ, Oskar Klein Ctr Cosmoparticle Phys, Dept Phys, Albanova Univ Ctr, SE-10691 Stockholm, Sweden.;Nordita SU.
    Belov, Pavel
    ITMO Univ, Sch Phys & Engn, St Petersburg 197101, Russia..
    Wire metamaterial filled metallic resonators2022Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, nr 7, artikel-id 075106Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this work we study electromagnetic properties of a resonator recently suggested for the search of axions-a hypothetical candidate to explain dark matter. A wire medium loaded resonator (called a plasma haloscope when used to search for dark matter) consists of a box filled with a dense array of parallel wires electrically connected to top and bottom walls. We show that the homogenization model of a wire medium works for this resonator without mesoscopic corrections, and that the resonator quality factor Q at the frequency of our interest drops versus the growth of the resonator volume V until it is dominated by resistive losses in the wires. We find that even at room temperature metals like copper can give quality factors in the thousands-an order of magnitude higher than originally assumed. Our theoretical results for both loaded and unloaded resonator quality factors were confirmed by building an experimental prototype. We discuss ways to further improve wire medium loaded resonators.

  • 15.
    Bandyopadhyay, Arka
    et al.
    Univ Calcutta, Dept Phys, 92 APC Rd, Kolkata 700009, India..
    Majumdar, Arnab
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Chowdhury, Suman
    Skolkovo Innovat Ctr, Skolkovo Inst Sci & Technol, 3 Nobel St, Moscow 121205, Russia..
    Ahuja, Rajeev
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Egenskaper. Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.
    Jana, Debnarayan
    Univ Calcutta, Dept Phys, 92 APC Rd, Kolkata 700009, India..
    8-16-4 graphyne: Square-lattice two-dimensional nodal line semimetal with a nontrivial topological Zak index2021Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, nr 7, artikel-id 075137Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An unprecedented graphyne allotrope with square symmetry and nodal line semimetallic behavior has been proposed in the two-dimensional (2D) realm. The emergence of the Dirac loop around the high-symmetry points in the presence of both the inversion and time-reversal symmetries is a predominant feature of the electronic band structure of this system. Besides, the structural stability in terms of the dynamic, thermal, and mechanical properties has been critically established for the system. Following the exact analytical model based on the realspace renormalization group scheme and tight-binding approach, we have inferred that the family of 2D nodal line semimetals with square symmetry can be reduced to a universal four-level system in the low-energy limit. This renormalized lattice indeed explains the underlying mechanism responsible for the fascinating emergence of 2D square nodal line semimetals. Besides, the analytical form of the generic dispersion relation of these systems is well supported by our density-functional theory results. Finally, the nontrivial topological properties have been explored for the predicted system without breaking the inversion and time-reversal symmetry of the lattice. We have obtained that the edge states are protected by the nonvanishing topological index, i.e., Zak phase.

  • 16.
    Banerjee, R.
    et al.
    Nanyang Technol Univ, Sch Phys & Math Sci, Div Phys & Appl Phys, Singapore 637371, Singapore..
    Liew, T. C. H.
    Nanyang Technol Univ, Sch Phys & Math Sci, Div Phys & Appl Phys, Singapore 637371, Singapore..
    Kyriienko, Oleksandr
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Realization of Hofstadter's butterfly and a one-way edge mode in a polaritonic system2018Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, nr 7, artikel-id 075412Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a scheme to generate an artificial gauge field for the system of neutral bosons, represented by polaritons in micropillars arranged into a square lattice. The splitting between the two polarizations of the micropillars breaks the time-reversal symmetry (TRS) and results in the effective phase-dependent hopping between cavities. This can allow for engineering a nonzero flux on the plaquette, corresponding to an artificial magnetic field. Changing the phase, we observe a characteristic Hofstadter's butterfly pattern and the appearance of chiral edge states for a finite-size structure. For long-lived polaritons, we show that the propagation of wave packets at the edge is robust against disorder. Moreover, given the inherent driven-dissipative nature of polariton lattices, we find that the system can exhibit topological lasing, recently discovered for active ring cavity arrays. The results point to a static way to realize artificial magnetic field in neutral spinful systems, avoiding the periodic modulation of the parameters or strong spin-orbit interaction. Ultimately, the described system can allow for high-power topological single-mode lasing which is robust to imperfections.

  • 17.
    Barkman, Mats
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Samoilenka, Albert
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Benfenati, Andrea
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Elevated critical temperature at BCS superconductor-band insulator interfaces2022Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, nr 22, artikel-id 224518Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider the interface between a Bardeen-Cooper-Schrieffer superconductor and nonsuperconducting band insulator. We show that under certain conditions, such interfaces can have an elevated superconducting critical temperature, without increasing the strength of the pairing interaction at the interface. We identify the regimes where the interface critical temperature exceeds the critical temperature associated with a superconductor vacuum interface.

  • 18.
    Barkman, Mats
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Zyuzin, Alexander A.
    Aalto Univ, Dept Appl Phys, POB 15100, FI-00076 Aalto, Finland.;Ioffe Phys Tech Inst, St Petersburg 194021, Russia..
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Antichiral and nematicity-wave superconductivity2019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 22, artikel-id 220508Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Larkin-Ovchinnikov superconducting state has spontaneous modulation of Cooper pair density, while Fulde-Ferrell state has a spontaneous modulation in the phase of the order parameter. We report that a quasi-two-dimensional Dirac metal, under certain conditions has principally different inhomogeneous superconducting states that by contrast have spontaneous modulation in a submanifold of a multiple-symmetries-breaking order parameter. The first state we find can be viewed as a nematic superconductor where the nematicity vector spontaneously breaks rotational and translational symmetries due to spatial modulation. The other demonstrated state is a chiral superconductor with spontaneously broken time-reversal and translational symmetries. It is characterized by an order parameter, which forms a lattice pattern of alternating chiralities.

  • 19. Behrends, Jan
    et al.
    Bardarson, Jens H.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori. Max Planck Institute, Germany.
    Strongly angle-dependent magnetoresistance in Weyl semimetals with long-range disorder2017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 6, artikel-id 060201Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The chiral anomaly in Weyl semimetals states that the left- and right-handed Weyl fermions, constituting the low energy description, are not individually conserved, resulting, for example, in a negative magnetoresistance in such materials. Recent experiments see strong indications of such an anomalous resistance response; however, with a response that at strong fields is more sharply peaked for parallel magnetic and electric fields than expected from simple theoretical considerations. Here, we uncover a mechanism, arising from the interplay between the angle-dependent Landau-level structure and long-range scalar disorder, that has the same phenomenology. In particular, we analytically show, and numerically confirm, that the internode scattering time decreases exponentially with the angle between the magnetic field and the Weyl node separation in the large field limit, while it is insensitive to this angle at weak magnetic fields. Since, in the simplest approximation, the internode scattering time is proportional to the anomaly-related conductivity, this feature may be related to the experimental observations of a sharply peaked magnetoresistance.

  • 20.
    Behrends, Jan
    et al.
    Max Planck Inst Phys Komplexer Syst, D-01187 Dresden, Germany.;Univ Cambridge, Cavendish Lab, TCM Grp, JJ Thomson Ave, Cambridge CB3 0HE, England..
    Bardarson, Jens H.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Beri, Benjamin
    Univ Cambridge, Cavendish Lab, TCM Grp, JJ Thomson Ave, Cambridge CB3 0HE, England.;Univ Cambridge, DAMTP, Wilberforce Rd, Cambridge CB3 0WA, England..
    Tenfold way and many-body zero modes in the Sachdev-Ye-Kitaev model2019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 19, artikel-id 195123Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Sachdev-Ye-Kitaev (SYK) model, in its simplest form, describes k Majorana fermions with random all-to-all four-body interactions. We consider the SYK model in the framework of a many-body Altland-Zirnbauer classification that sees the system as belonging to one of eight (real) symmetry classes depending on the value of k mod 8. We show that, depending on the symmetry class, the system may support exact many-body zero modes with the symmetries also dictating whether these may have a nonzero contribution to Majorana fermions, i.e., single-particle weight. These zero modes appear in all but two of the symmetry classes. When present, they leave clear signatures in physical observables that go beyond the threefold (Wigner-Dyson) possibilities for level spacing statistics studied earlier. Signatures we discover include a zero-energy peak or hole in the single-particle spectral function, depending on whether symmetries allow or forbid zero modes to have single-particle weight. The zero modes are also shown to influence the many-body dynamics, where signatures include a nonzero long-time limit for the out-of-time-order correlation function. Furthermore, we show that the extension of the four-body SYK model by quadratic terms can be interpreted as realizing the remaining two complex symmetry classes; we thus demonstrate how the entire tenfold Altland-Zirnbauer classification may emerge in the SYK model.

  • 21. Behrends, Jan
    et al.
    Rhim, Jun-Won
    Liu, Shang
    Grushin, Adolfo G.
    Bardarson, Jens H.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori. Max-Planck-Institut für Physik Komplexer Systeme, Germany.
    Nodal-line semimetals from Weyl superlattices2017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 24, artikel-id 245101Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The existence and topological classification of lower-dimensional Fermi surfaces is often tied to the crystal symmetries of the underlying lattice systems. Artificially engineered lattices, such as heterostructures and other superlattices, provide promising avenues to realize desired crystal symmetries that protect lower-dimensional Fermi surfaces, such as nodal lines. In this work, we investigate a Weyl semimetal subjected to spatially periodic onsite potential, giving rise to several phases, including a nodal-line semimetal phase. In contrast to proposals that purely focus on lattice symmetries, the emergence of the nodal line in this setup does not require small spin-orbit coupling, but rather relies on its presence. We show that the stability of the nodal line is understood from reflection symmetry and a combination of a fractional lattice translation and charge-conjugation symmetry. Depending on the choice of parameters, this model exhibits drumhead surface states that are exponentially localized at the surface, or weakly localized surface states that decay into the bulk at all energies.

  • 22.
    Behrends, Jan
    et al.
    Max Planck Inst Phys Komplexer Systeme, D-01187 Dresden, Germany..
    Roy, Sthitadhi
    Max Planck Inst Phys Komplexer Systeme, D-01187 Dresden, Germany.;Univ Oxford, Phys & Theoret Chem, South Parks Rd, Oxford OX1 3QZ, England.;Univ Oxford, Rudolf Peierls Ctr Theoret Phys, Clarendon Lab, Parks Rd, Oxford OX1 3PU, England..
    Kolodrubetz, Michael H.
    Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA.;Lawrence Berkeley Natl Lab, Mat Sci Div, Berkeley, CA 94720 USA.;Univ Texas Dallas, Dept Phys, Richardson, TX 75080 USA..
    Bardarson, Jens H.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori. Max Planck Inst Phys Komplexer Systeme, D-01187 Dresden, Germany.
    Grushin, Adolfo G.
    Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA.;CNRS, Inst Neel, F-38042 Grenoble, France.;Univ Grenoble Alpes, F-38042 Grenoble, France..
    Landau levels, Bardeen polynomials, and Fermi arcs in Weyl semimetals: Lattice-based approach to the chiral anomaly2019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 14, artikel-id 140201Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Condensed matter systems realizing Weyl fermions exhibit striking phenomenology derived from their topologically protected surface states as well as chiral anomalies induced by electromagnetic fields. More recently, inhomogeneous strain or magnetization were predicted to result in chiral electric E-5 and magnetic B-5 fields, which modify and enrich the chiral anomaly with additional terms. In this Rapid Communication, we develop a lattice-based approach to describe the chiral anomaly, which involves Landau and pseudo-Landau levels and treats all anomalous terms on equal footing, while naturally incorporating Fermi arcs. We exemplify its potential by physically interpreting the largely overlooked role of Fermi arcs in the covariant (Fermi level) contribution to the anomaly and revisiting the factor of 1/3 difference between the covariant and consistent (complete band) contributions to the E-5 . B-5 term in the anomaly. Our framework provides a versatile tool for the analysis of anomalies in realistic lattice models as well as a source of simple physical intuition for understanding strained and magnetized inhomogeneous Weyl semimetals.

  • 23.
    Belonoshko, Anatoly
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori. Natl Res Univ Higher Sch Econ, Moscow 123458, Russia..
    Fu, Jie
    Ningbo Univ, Sch Phys Sci & Technol, Dept Phys, Ningbo 315211, Peoples R China..
    Smirnov, Grigory
    Natl Res Univ Higher Sch Econ, Moscow 123458, Russia.;Russian Acad Sci, Joint Inst High Temp, Moscow 125412, Russia..
    Free energies of iron phases at high pressure and temperature: Molecular dynamics study2021Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, nr 10, artikel-id 104103Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The crystal structure of iron, the major component of the Earth's inner core (IC), is unknown under the IC high pressure (P) (3.3-3.6 Mbar) and temperature (T) (5000-7000 K). Experimental and theoretical data on the phase diagram of iron at these extreme PT conditions are contradictory. Applying quasi-ab initio and ab initio molecular dynamics we computed free energies of the body-centered cubic (bcc), hexagonal close-packed (hcp), and liquid phases. The ionic free energies, computed for the embedded-atom model, were corrected for electronic entropy. Such correction brings the melting temperatures of the hcp iron in very good agreement with previous ab initio data. This validates the calculation of the bcc phase, where fully ab initio treatment is not technically possible due to large sizes required for convergence. The resulting phase diagram shows stabilization of the bcc phase prior to melting in the pressure range of the IC. The melting temperature of the bcc phase is equal to 7190 K at the pressure 360 GPa.

  • 24.
    Belonoshko, Anatoly
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Simak, S. I.
    Olovsson, W.
    Vekilova, O. Y.
    Elastic properties of body-centered cubic iron in Earth's inner core2022Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, nr 18, artikel-id L180102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The solid Earth's inner core (IC) is a sphere with a radius of about 1300 km in the center of the Earth. The information about the IC comes mainly from seismic studies. The composition of the IC is obtained by matching the seismic data and properties of candidate phases subjected to high pressure (P) and temperature (T). The close match between the density of the IC and iron suggests that the main constituent of the IC is iron. However, the stable phase of iron is still a subject of debate. One such iron phase, the body-centered cubic phase (bcc), is dynamically unstable at pressures of the IC (330-364 GPa) and low T but gets stabilized at high T characteristic of the IC (5000-7000 K). So far, ab initio molecular dynamics (AIMD) studies attempted to compute the bcc elastic properties for a small (order of 102) number of atoms. The mechanism of the bcc stabilization cannot be enabled in such cells and that has led to erroneous results. Here we apply AIMD to compute elastic moduli and sound velocities of the Fe bcc phase for a 2000 Fe atom computational cell, which is a cell of unprecedented size for ab initio calculations of iron. Unlike in previous ab initio calculations, both the longitudinal and the shear sound velocities of the Fe bcc phase closely match the properties of the IC material at P = 360 GPa and T = 6600 K, likely the PT conditions in the IC. The calculated density of the bcc iron at these PT conditions is just 3% higher than the density of the IC material according to the Preliminary Earth Model. This suggests that the widely assumed amount of light elements in the IC may need a reconsideration. The anisotropy of the bcc phase is an exact match to the most recent seismic studies. 

  • 25.
    Benfenati, Andrea
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Spontaneous edge and corner currents in s+is superconductors and time reversal symmetry breaking surface states2022Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, nr 13, s. 134518-, artikel-id PhysRevB.105.134518Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a study of the basic microscopic model of a s-wave superconductor with frustrated interbandinteraction. When frustration is strong, such an interaction gives raise to a s + is state. This is a s-wave superconductor that spontaneously breaks time reversal symmetry. We show that in addition to the known s + is state,there is additional phase where the system’s bulk is a conventional s-wave state, but superconducting surfacestates break time reversal symmetry. Furthermore, we show that s + is superconductors can have spontaneousboundary currents and spontaneous magnetic fields. These arise at lower-dimensional boundaries, namely, thecorners in two-dimensional samples. This demonstrates that boundary currents effects in superconductors canarise in states which are not topological and not chiral according to the modern classification.

  • 26.
    Benfenati, Andrea
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Barkman, Mats
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Demonstration of CP2 skyrmions in three-band superconductors by self-consistent solutions of a Bogoliubov-de Gennes model2023Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, nr 9, artikel-id 094503Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Topological defects, such as magnetic-flux-carrying quantum vortices, determine the magnetic response of superconductors and hence are of fundamental importance. Here, we show that stable CP2 skyrmions exist in three-band s + is superconductors as fully self-consistent solutions to a microscopic Bogoliubov-de Gennes model. This allows us to calculate microscopically the magnetic signatures of CP2 skyrmions and their footprint in the local density of states.

  • 27.
    Benfenati, Andrea
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Barkman, Mats
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Winyard, Thomas
    Univ Leeds, Sch Math, Leeds LS2 9JT, W Yorkshire, England..
    Wormald, Alex
    School of Mathematics, University of Leeds, Leeds, LS2 9JT, United Kingdom.
    Speight, Martin
    Univ Leeds, Sch Math, Leeds LS2 9JT, W Yorkshire, England..
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Magnetic signatures of domain walls in s plus is and s plus id superconductors: Observability and what that can tell us about the superconducting order parameter2020Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, nr 5, artikel-id 054507Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    One of the defining features of spontaneously broken time-reversal symmetry (BTRS) is the existence of domain walls, the detection of which would be strong evidence for such systems. There is keen interest in BTRS currently, in part, due to recent muon spin rotation experiments, which have pointed towards Ba1-xKxFe2As2 exhibiting a remarkable case of s-wave superconductivity with spontaneously broken time-reversal symmetry. A key question, however, is how to differentiate between the different theoretical models which describe such a state. Two particularly popular choices of model are s + is and s + id superconducting states. In this paper, we obtain solutions for domain walls in s + is and s + id systems, including the effects of lattice anisotropies. We show that, in general, both models exhibit spontaneous magnetic fields that extend along the entire length of the domain wall. We demonstrate the qualitative difference between the magnetic signatures of s + is and s + id domain walls and propose a procedure to extract the superconducting pairing symmetry from the magnetic-field response of domain walls.

  • 28.
    Benfenati, Andrea
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Maiani, Andrea
    KTH, Skolan för teknikvetenskap (SCI).
    Rybakov, Filipp N.
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Statistisk fysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Vortex nucleation barrier in superconductors beyond the Bean-Livingston approximation: A numerical approach for the sphaleron problem in a gauge theory2020Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, nr 22, artikel-id 220505Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The knowledge of vortex nucleation barriers is crucial for applications of superconductors, such as single-photon detectors and superconductor-based qubits. Contrarily to the problem of finding energy minima and critical fields, there are no controllable methods to explore the energy landscape, identify saddle points, and compute associated barriers. Similar problems exist in high-energy physics where the saddle-point configurations are called sphalerons. Here, we present a generalization of the string method to gauge field theories, which allows the calculation of energy barriers in superconductors. We solve the problem of vortex nucleation, assessing the effects of the nonlinearity of the model, complicated geometry, surface roughness, and pinning.

  • 29.
    Benfenati, Andrea
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Samoilenka, Albert
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Boundary effects in two-band superconductors2021Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, nr 14, artikel-id 144512Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a microscopic study of the behavior of the order parameters near the boundaries of a two-band superconducting material, described by the standard tight-binding Bardeen-Cooper-Schrieffer model. We find superconducting surface states. The relative difference between bulk and surface critical temperatures is a nontrivial function of the interband coupling strength. For superconductors with weak interband coupling, boundaries induce variations of the gaps with the presence of multiple length scales, despite nonzero interband Josephson coupling.

  • 30.
    Berntson, Bjorn K.
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.).
    Langmann, Edwin
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Matematisk fysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Lenells, Jonatan
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.), Matematik (Avd.).
    Nonchiral intermediate long-wave equation and interedge effects in narrow quantum Hall systems2020Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, nr 15, artikel-id 155308Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a nonchiral version of the intermediate long-wave (ILW) equation that can model nonlinear waves propagating on two opposite edges of a quantum Hall system, taking into account interedge interactions. We obtain exact soliton solutions governed by the hyperbolic Calogero-Moser-Sutherland (CMS) model, and we give a Lax pair, a Hirota form, and conservation laws for this new equation. We also present a periodic nonchiral ILW equation, together with its soliton solutions governed by the elliptic CMS model.

  • 31.
    Bhalla, Pankaj
    et al.
    NORDITA, SU; Stockholm Univ, Hannes Alfvens vag 12, S-11421 Stockholm, Sweden..
    Rostami, Habib
    Second harmonic helicity and Faraday rotation in gated single-layer 1T ' -WTe22022Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, nr 23, artikel-id 235132Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A single layer of the 1T' phase of WTe2 provides a rich platform for exotic physical properties such as the nonlinear Hall effect and high-temperature quantum spin Hall transport. Utilizing a continuum model and the diagrammatic method, we calculate the second harmonic conductivity of monolayer 1T'-WTe2 modulated by an external vertical electric field and electron doping. We obtain a finite helicity and Faraday rotation for the second harmonic signal in response to linearly polarized incident light in the presence of time-reversal symmetry. The second harmonic signal's helicity is highly controllable by altering the bias potential and serves as an optical indicator of the nonlinear Hall current. Our study motivates future experimental investigation of the helicity spectroscopy of two-dimensional materials.

  • 32.
    Bhalla, Pankaj
    et al.
    Nordita SU; Stockholm Univ, Hannes Alfvens Vag 12, S-10691 Stockholm, Sweden..
    Vignale, Giovanni
    Univ Missouri, Dept Phys & Astron, Columbia, MO 65211 USA..
    Rostami, Habib
    Nordita SU;Stockholm Univ, Hannes Alfvens Vag 12, S-10691 Stockholm, Sweden..
    Pseudogauge field driven acoustoelectric current in two-dimensional hexagonal Dirac materials2022Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, nr 12, artikel-id 125407Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using a diagrammatic scheme, we study the acoustoelectric effects in two-dimensional (2D) hexagonal Dirac materials due to the sound-induced pseudogauge field. We analyze both uniform and spatially dispersive currents in response to copropagating and counterpropagating sound waves, respectively. In addition to the longitudinal acoustoelectric current, we obtain an exotic transverse charge current flowing perpendicular to the sound propagation direction owing to the interplay of transverse and longitudinal gauge field components j(T) proportional to A(L)A(T)*. In contrast to the almost isotropic directional profile of the longitudinal uniform current, a highly anisotropic transverse component j(T) similar to sin(6 theta) is achieved that stems from the inherited threefold symmetry of the hexagonal lattice. However, both longitudinal and transverse parts of the dispersive current are predicted to be strongly anisotropic similar to sin(2)(theta) or cos(2)(3 theta). We quantitatively estimate the pseudogauge field contribution to the acoustoelectric current that can be probed in future experiments in graphene and other 2D hexagonal Dirac materials.

  • 33. Biswas, P. K.
    et al.
    Rybakov, Filipp N.
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Kondenserade materiens teori.
    Singh, R. P.
    Mukherjee, Saumya
    Parzyk, N.
    Balakrishnan, G.
    Lees, M. R.
    Dewhurst, C. D.
    Babaev, Egor
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Hillier, A. D.
    Paul, D. Mc K.
    Coexistence of type-I and type-II superconductivity signatures in ZrB12 probed by muon spin rotation measurements2020Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, nr 14, artikel-id 144523Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Superconductors usually display either type-I or type-II superconductivity and the coexistence of these two types in the same material, for example, at different temperatures, is rare in nature. We employed the muon spin rotation (mu SR) technique to unveil the superconducting phase diagram of the dodecaboride ZrB12 and obtained clear evidence of both type-I and type-II characteristics. Most important, we found a region showing unusual behavior where the usually mutually exclusive mu SR signatures of type-I and type-II superconductivity coexist. We reproduced that behavior in theoretical modeling that required taking into account multiple bands and multiple coherence lengths, which suggests that material has one coherence length larger and another smaller than the magnetic field penetration length (the type-1.5 regime). At stronger fields, a footprint of the type-II mixed state showing square flux-line lattice was also obtained using neutron diffraction.

  • 34. Bjornson, Kristofer
    et al.
    Balatsky, Alexander V.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. os Alamos National Laboratory, United States; ETH Institute for Theoretical Studies, Switzerland.
    Black-Schaffer, Annica M.
    Superconducting order parameter pi-phase shift in magnetic impurity wires2017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, nr 10, artikel-id 104521Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It has previously been found that amagnetic impurity in a conventional s-wave superconductor can give rise to a local pi-phase shift of the superconducting order parameter. By studying a finite wire of ferromagnetic impurities, we are able to trace the origin of the pi-phase shift to a resonance condition for the Bogoliubov-de Gennes quasiparticle states. When nonresonating states localized at the impurity sites are pulled into the condensate for increasing magnetic strength, the superconducting order parameter is reduced in discrete steps, eventually resulting in a pi-phase shift. We also show that for a finite spin-orbit coupling, the pi-phase shift is preserved and occurs in a large portion of the topologically nontrivial phase.

  • 35.
    Bondarenko, Artem
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Holmgren, Erik
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Li, Zhong Wei
    Ivanov, B. A.
    Institute of Magnetism, National Academy of Science, 03142 Kiev, Ukraine; National University of Science and Technology “MISiS”, Moscow 119049, Russian Federation..
    Korenivski, Vladislav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Nanostrukturfysik.
    Chaotic dynamics in spin-vortex pairs2019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, artikel-id 054402Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on spin-vortex pair dynamics measured at temperatures low enough to suppress stochastic core motion, thereby uncovering the highly nonlinear intrinsic dynamics of the system. Our analysis shows that the decoupling of the two vortex cores is resonant and can be enhanced by dynamic chaos. We detail the regions of the relevant parameter space, in which the various mechanisms of the resonant core-core dynamics are activated. We show that the presence of chaos can reduce the thermally induced spread in the decoupling time by up to two orders of magnitude.

  • 36.
    Bondarenko, N.
    et al.
    Uppsala Univ, Dept Phys & Astron, Div Mat Theory, Box 516, SE-75121 Uppsala, Sweden..
    Chico, J.
    Uppsala Univ, Dept Phys & Astron, Div Mat Theory, Box 516, SE-75121 Uppsala, Sweden.;Forschungszentrum Julich, Peter Grunberg Inst, D-52428 Julich, Germany.;Forschungszentrum Julich, Inst Adv Simulat, D-52428 Julich, Germany.;JARA, D-52428 Julich, Germany..
    Kvashnin, Y. O.
    Uppsala Univ, Dept Phys & Astron, Div Mat Theory, Box 516, SE-75121 Uppsala, Sweden..
    Bergman, A.
    Uppsala Univ, Dept Phys & Astron, Div Mat Theory, Box 516, SE-75121 Uppsala, Sweden.;Univ Versailles, Univ Paris Sud, CNRS, Maison Simulat,CEA,INRIA,USR 3441, F-91191 Gif Sur Yvette, France.;CEA, INAC MEM, L Sim, F-38000 Grenoble, France..
    Skorodumova, Natalia
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering. Uppsala Univ, Dept Phys & Astron, Div Mat Theory, Box 516, SE-75121 Uppsala, Sweden.
    Eriksson, O.
    Uppsala Univ, Dept Phys & Astron, Div Mat Theory, Box 516, SE-75121 Uppsala, Sweden.;Orebro Univ, Sch Sci & Technol, SE-70182 Orebro, Sweden..
    Spin polaronics: Static and dynamic properties of spin polarons in La-doped CaMnO42019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, nr 13, artikel-id 134443Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The static and dynamic properties of spin polarons in La-doped CaMnO3 are explored theoretically, by means of an effective low-energy Hamiltonian. All parameters of the effective Hamiltonian are evaluated from first-principles theory. The Hamiltonian is used to investigate the temperature stability as well as the response to an external applied electric field, for spin polarons in bulk, surface, and as single two-dimensional layers. Technically this involves atomistic spin-dynamics simulations in combination with kinetic Monte Carlo simulations. Where a comparison can be made, our simulations exhibit excellent agreement with available experimental data and previous theory. Remarkably, we find that excellent control of the mobility of spin polarons in this material can be achieved, and that the critical parameters deciding this are the temperature and strength of the applied electrical field. We outline different technological implications of spin polarons, and point to spin polaronics as an emerging subfield of nanotechnology. In particular, we demonstrate that it is feasible to write and erase information on an atomic scale, by use of spin polarons in CaMnO3.

  • 37. Bondarenko, N.
    et al.
    Kvashnin, Y.
    Chico, J.
    Bergman, A.
    Eriksson, O.
    Skorodumova, Natalia V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Flerskalig materialmodellering. Uppsala Univ, Sweden.
    Spin-polaron formation and magnetic state diagram in La-doped CaMnO32017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, nr 22, artikel-id 220401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    LaxCa1-xMnO3 (LCMO) has been studied in the framework of density functional theory (DFT) using Hubbard-U correction. We show that the formation of spin polarons of different configurations is possible in the G-type antiferromagnetic phase. We also show that the spin-polaron (SP) solutions are stabilized due to an interplay of magnetic and lattice effects at lower La concentrations and mostly due to the lattice contribution at larger concentrations. Our results indicate that the development of SPs is unfavorable in the C- and A-type antiferromagnetic phases. The theoretically obtained magnetic state diagram is in good agreement with previously reported experimental results.

  • 38.
    Borisov, Vladislav
    et al.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Kvashnin, Yaroslav O.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Ntallis, Nikolaos
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Thonig, Danny
    Örebro Univ, Sch Sci & Technol, SE-70182 Örebro, Sweden..
    Thunström, Patrik
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Pereiro, Manuel
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Bergman, Anders
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Sjöqvist, Erik
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Delin, Anna
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Nordström, Lars
    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, SE-70182 Örebro, Sweden..
    Heisenberg and anisotropic exchange interactions in magnetic materials with correlated electronic structure and significant spin-orbit coupling2021Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, nr 17, artikel-id 174422Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Dzyaloshinskii-Moriya (DM) interaction, as well as symmetric anisotropic exchange, are important ingredients for stabilizing topologically nontrivial magnetic textures, such as, e.g., skyrmions, merons, and hopfions. These types of textures are currently in focus from a fundamental science perspective and they are also discussed in the context of future spintronics information technology. While the theoretical understanding of the Heisenberg exchange interactions is well developed, it is still a challenge to access, from first principles theory, the DM interaction as well as the symmetric anisotropic exchange, which both require a fully-relativistic treatment of the electronic structure, in magnetic systems where substantial electron-electron correlations are present. Here, we present results of a theoretical framework which allows to compute these interactions in any given system and demonstrate its performance for several selected cases, for both bulk and low-dimensional systems. We address several representative cases, including the bulk systems CoPt and FePt, the B20 compounds MnSi and FeGe as well as the low-dimensional transition metal bilayers Co/Pt(111) andMn/W(001). The effect of electron-electron correlations is analyzed using dynamical mean-field theory on the level of the spin-polarized T -matrix + fluctuating exchange (SPTF) approximation, as regards the strength and character of the isotropic (Heisenberg) and anisotropic (DM) interactions in relation to the underlying electronic structure. Our method can be combined with more advanced techniques for treating correlations, e.g., quantum Monte Carlo and exact diagonalization methods for the impurity solver of dynamical mean-field theory. We find that correlation-induced changes of the DM interaction can be rather significant, with up to fivefold modifications in the most distinctive case.

  • 39. Borlenghi, Simone
    et al.
    Mahani, M. Reza
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF.
    Delin, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik, Materialfysik, MF. KTH, Centra, SeRC - Swedish e-Science Research Centre. Uppsala University, Sweden.
    Fransson, Jonas
    Nanoscale control of heat and spin conduction in artificial spin chains2016Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, nr 13, artikel-id 134419Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We describe a mechanism to control the energy and magnetization currents in an artificial spin chain, consisting of an array of permalloy nanodisks coupled through a magnetodipolar interaction. The chain is kept out of equilibrium by two thermal baths with different temperatures connected to its ends, which control the current propagation. Transport is enhanced by applying a uniform radio-frequency pump field resonating with some of the spin-wave modes of the chain. Moreover, the two currents can be controlled independently by tuning the static field applied on the chain. Thus we describe two effective means for the independent control of coupled currents and the enhancement of thermal and spin-wave conductivity in a realistic magnonics device, suggesting that similar effects could be observed in a large class of nonlinear oscillating systems.

  • 40. Borlenghi, Simone
    et al.
    Mahani, Mohammad Reza
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Fangohr, Hans
    Franchin, M.
    Delin, Anna
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Material- och nanofysik. KTH, Centra, SeRC - Swedish e-Science Research Centre. Uppsala Univ, Sweden.
    Fransson, Jonas
    Micromagnetic simulations of spin-torque driven magnetization dynamics with spatially resolved spin transport and magnetization texture2017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, nr 9, artikel-id 094428Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a simple and fast method to simulate spin-torque driven magnetization dynamics in nanopillar spin-valve structures. The approach is based on the coupling between a spin transport code based on random matrix theory and a micromagnetics finite-elements software. In this way the spatial dependence of both spin transport and magnetization dynamics is properly taken into account. Our results are compared with experiments. The excitation of the spin-wave modes, including the threshold current for steady-state magnetization precession and the nonlinear frequency shift of the modes are reproduced correctly. The giant magneto resistance effect and the magnetization switching also agree with experiment. The similarities with recently described spin-caloritronics devices are also discussed.

  • 41. Bostrom, Mathias
    et al.
    Malyi, Oleksandr I.
    Parashar, Prachi
    Shajesh, K. V.
    Thiyam, Priyadarshini
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Milton, Kimball A.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. University of Oslo, Norway.
    Parsons, Drew F.
    Brevik, Iver
    Lifshitz interaction can promote ice growth at water-silica interfaces2017Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, nr 15, artikel-id 155422-1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    At air-water interfaces, the Lifshitz interaction by itself does not promote ice growth. On the contrary, we find that the Lifshitz force promotes the growth of an ice film, up to 1-8 nm thickness, near silica-water interfaces at the triple point of water. This is achieved in a system where the combined effect of the retardation and the zero frequency mode influences the short-range interactions at low temperatures, contrary to common understanding. Cancellation between the positive and negative contributions in the Lifshitz spectral function is reversed in silica with high porosity. Our results provide a model for how water freezes on glass and other surfaces.

  • 42.
    Boström, M.
    et al.
    Centre of Excellence ENSEMBLE 3 Sp. z o. o., Wolczynska Str. 133, 01-919 Warsaw, Poland.
    Khan, M. R.
    Centre of Excellence ENSEMBLE 3 Sp. z o. o., Wolczynska Str. 133, 01-919 Warsaw, Poland.
    Gopidi, H. R.
    Centre of Excellence ENSEMBLE 3 Sp. z o. o., Wolczynska Str. 133, 01-919 Warsaw, Poland.
    Brevik, I.
    Department of Energy and Process Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
    Li, Y.
    Department of Physics, Nanchang University, Nanchang 330031, China; Institute of Space Science and Technology, Nanchang University, Nanchang 330031, China.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer. Centre for Materials Science and Nanotechnology, Department of Physics, University of Oslo, P. O. Box 1048 Blindern, NO-0316 Oslo, Norway.
    Malyi, O. I.
    Centre of Excellence ENSEMBLE 3 Sp. z o. o., Wolczynska Str. 133, 01-919 Warsaw, Poland.
    Tuning the Casimir-Lifshitz force with gapped metals2023Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, nr 16, artikel-id 165306Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Casimir-Lifshitz interaction, a long-range force that arises between solids and molecules due to quantum fluctuations in electromagnetic fields, has been widely studied in solid-state physics. The degree of polarization in this interaction is influenced by the dielectric properties of the materials involved, which in turn are determined by factors such as band-to-band transitions, free carrier contributions, phonon contributions, and exciton contributions. Gapped metals, a new class of materials with unique electronic structures, offer the potential to manipulate dielectric properties and, consequently, the Casimir-Lifshitz interaction. In this study, we theoretically investigate the finite temperature Casimir-Lifshitz interaction in La3Te4-based gapped metal systems with varying off-stoichiometry levels. We demonstrate that off-stoichiometric effects in gapped metals can be used to control the magnitude and, in some cases, even the sign of Casimir-Lifshitz interactions. We predict measurable corrections due to stoichiometry on the predicted Casimir force between a La3Te4 surface and a gold sphere, attached to an atomic force microscopy tip.

  • 43.
    Boström, M.
    et al.
    Centre of Excellence ENSEMBLE3 Sp. z o. o., Wolczynska Str. 133, 01-919 Warsaw, Poland.
    Kuthe, Sudhanshu
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Carretero-Palacios, S.
    Departamento de Física de Materiales and Instituto de Materiales Nicolás Cabrera, Universidad Autónoma de Madrid, 28049 Madrid, Spain; Present address: Instituto de Ciencia de Materiales de Madrid, ICMM-CSIC, C/Sor Juana Inés de la Cruz, 3, 28049 Madrid, Spain.
    Esteso, V.
    Departamento de Física de la Materia Condensada, ICMSE-CSIC, Universidad de Sevilla, Apdo. 1065, Sevilla, Spain; European Laboratory for Non-Linear Spectroscopy (LENS), Via Nello Carrara 1, Sesto F.no 50019, Italy.
    Li, Y.
    Department of Physics, Nanchang University, Nanchang 330031, China; Institute of Space Science and Technology, Nanchang University, Nanchang 330031, China.
    Brevik, I.
    Department of Energy and Process Engineering, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
    Gopidi, H. R.
    Centre of Excellence ENSEMBLE3 Sp. z o. o., Wolczynska Str. 133, 01-919 Warsaw, Poland.
    Malyi, O. I.
    Centre of Excellence ENSEMBLE3 Sp. z o. o., Wolczynska Str. 133, 01-919 Warsaw, Poland.
    Glaser, Björn
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Processer.
    Persson, Clas
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap. Centre for Materials Science and Nanotechnology, Department of Physics, University of Oslo, P. O. Box 1048 Blindern, NO-0316 Oslo, Norway.
    Understanding ice and water film formation on soil particles by combining density functional theory and Casimir-Lifshitz forces2023Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, nr 12, artikel-id 125434Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Thin films of ice and water on soil particles play crucial roles in environmental and technological processes. Understanding the fundamental physical mechanisms underlying their formation is essential for advancing scientific knowledge and engineering practices. Herein, we focus on the role of the Casimir-Lifshitz force, also referred to as dispersion force, in the formation and behavior of thin films of ice and water on soil particles at 273.16 K, arising from quantum fluctuations of the electromagnetic field and depending on the dielectric properties of interacting materials. We employ the first-principles density functional theory (DFT) to compute the dielectric functions for two model materials, CaCO3 and Al2O3, essential constituents in various soils. These dielectric functions are used with the Kramers-Kronig relationship and different extrapolations to calculate the frequency-dependent quantities required for determining forces and free energies. Moreover, we assess the accuracy of the optical data based on the DFT to model dispersion forces effectively, such as those between soil particles. Our findings reveal that moisture can accumulate into almost micron-sized water layers on the surface of calcite (soil) particles, significantly impacting the average dielectric properties of soil particles. This research highlights the relevance of DFT-based data for understanding thin film formation in soil particles and offers valuable insights for environmental and engineering applications.

  • 44.
    Bouhon, Adrien
    et al.
    Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden.;Uppsala Univ, Dept Phys & Astron, Box 516, SE-75121 Uppsala, Sweden.;Nordita SU.
    Bzdusek, Tomas
    Paul Scherrer Inst, Condensed Matter Theory Grp, CH-5232 Villigen, Switzerland.;Univ Zurich, Dept Phys, Winterthurerstr 190, CH-8057 Zurich, Switzerland..
    Slager, Robert-Jan
    Univ Cambridge, Cavendish Lab, TCM Grp, JJ Thomson Ave, Cambridge CB3 0HE, England.;Harvard Univ, Dept Phys, Cambridge, MA 02138 USA..
    Geometric approach to fragile topology beyond symmetry indicators2020Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, nr 11, artikel-id 115135Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a framework to systematically address topological phases when finer partitionings of bands are taken into account, rather than only considering the two subspaces spanned by valence and conduction bands. Focusing on C2T-symmetric systems that have gained recent attention, for example, in the context of layered van-der-Waals graphene heterostructures, we relate these insights to homotopy groups of Grassmannians and flag varieties, which in turn correspond to cohomology classes and Wilson-flow approaches. We furthermore make use of a geometric construction, the so-called Plucker embedding, to induce windings in the band structure necessary to facilitate nontrivial topology. Specifically, this directly relates to the parametrization of the Grassmannian, which describes partitioning of an arbitrary band structure and is embedded in a better manageable exterior product space. From a physical perspective, our construction encapsulates and elucidates the concepts of fragile topological phases beyond symmetry indicators as well as non-Abelian reciprocal braiding of band nodes that arises when the multiple gaps are taken into account. The adopted geometric viewpoint most importantly culminates in a direct and easily implementable method to construct model Hamiltonians to study such phases, constituting a versatile theoretical tool.

  • 45. Boyko, D.
    et al.
    Balatsky, Alexander V.
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA. Los Alamos National Laboratory, United States.
    Haraldsen, J. T.
    Evolution of magnetic Dirac bosons in a honeycomb lattice2018Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, nr 1, artikel-id 014433Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We examine the presence and evolution of magnetic Dirac nodes in the Heisenberg honeycomb lattice. Using linear spin theory, we evaluate the collinear phase diagram as well as the change in the spin dynamics with various exchange interactions. We show that the ferromagnetic structure produces bosonic Dirac and Weyl points due to the competition between the interactions. Furthermore, it is shown that the criteria for magnetic Dirac nodes are coupled to the magnetic structure and not the overall crystal symmetry, where the breaking of inversion symmetry greatly affects the antiferromagnetic configurations. The tunability of the nodal points through variation of the exchange parameters leads to the possibility of controlling Dirac symmetries through an external manipulation of the orbital interactions.

  • 46.
    Bugaiko, O. V.
    et al.
    Faculty of Physics, Kyiv National Taras Shevchenko University, 64/13 Volodymyrska st., 01601 Kyiv, Ukraine.
    Gorbar, E. V.
    Faculty of Physics, Kyiv National Taras Shevchenko University, 64/13 Volodymyrska st., 01601 Kyiv, Ukraine 2Bogolyubov Institute for Theoretical Physics, Kyiv, 03680, Ukraine.
    Sukhachov, P. O.
    Nordita SU.
    Surface plasmon polaritons in strained Weyl semimetals2020Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, nr 8, artikel-id 085426Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Surface plasmon polaritons in a strained slab of a Weyl semimetal with broken time-reversal symmetry are investigated. It is found that the strain-induced axial gauge field reduces frequencies of these collective modes for intermediate values of the wave vector. Depending on the relative orientation of the separation of Weyl nodes in momentum space, the surface normal, and the direction of propagation, the dispersion relation of surface plasmon polaritons could be nonreciprocal even in a thin slab. In addition, strain-induced axial gauge fields can significantly affect the localization properties of the collective modes. These effects allow for an in situ control of the propagation of surface plasmon

  • 47.
    Burgos-Parra, Erick
    et al.
    Univ Exeter, Dept Phys & Astron, Exeter EX4 4QL, Devon, England..
    Keatley, Paul S.
    Univ Exeter, Dept Phys & Astron, Exeter EX4 4QL, Devon, England..
    Redjai Sani, Sohrab
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Durrenfeld, Phillip
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Åkerman, Johan
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik.
    Hicken, Robert J.
    Univ Exeter, Dept Phys & Astron, Exeter EX4 4QL, Devon, England..
    Time-resolved imaging of magnetization dynamics in double nanocontact spin torque vortex oscillator devices2019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, nr 13, artikel-id 134439Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Double nanocontact (NC) spin transfer vortex oscillator devices, in which NCs of 100-nm diameter have center-to-center separation ranging from 200 to 1100 nm, have been studied by means of electrical measurements and time-resolved scanning Kerr microscopy (TRSKM). The NCs were positioned close to the edge of the top electrical contact so that the magnetization dynamics of the adjacent region could be probed optically. The electrical measurements showed different ranges of frequency operation for devices with different NC separations. For 900-nm NC separation, TRSKM showed magnetic contrast consistent with the formation of a magnetic vortex at each NC, while for 200-nm NC separation a lack of magnetic contrast near the NC region suggests that the magnetization dynamics occur closer to the NC and underneath the top contact. TRSKM also reveals the presence of additional localized dynamical features far from the NCs, which are not seen by electrical measurements; has not been reported previously for double NCs with different separations; and provides insight into how the dynamic state of the phase-locked oscillators is established and stabilized.

  • 48.
    Calugaru, Dumitru
    et al.
    Max Planck Inst Phys Komplexer Syst, Nothnitzer Str 38, D-01187 Dresden, Germany.;Univ Cambridge, Cavendish Lab, JJ Thomson Ave, Cambridge CB3 0HE, England..
    Juricic, Vladimir
    KTH, Centra, Nordic Institute for Theoretical Physics NORDITA.
    Roy, Bitan
    Max Planck Inst Phys Komplexer Syst, Nothnitzer Str 38, D-01187 Dresden, Germany..
    Higher-order topological phases: A general principle of construction2019Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, nr 4, artikel-id 041301Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a general principle for constructing higher-order topological (HOT) phases. We argue that if a D-dimensional first-order or regular topological phase involves m Hermitian matrices that anticommute with additional p - 1 mutually anticommuting matrices, it is conceivable to realize an nth-order HOT phase, where n = 1, ..., p, with appropriate combinations of discrete symmetry-breaking Wilsonian masses. An nth-order HOT phase accommodates zero modes on a surface with codimension n. We exemplify these scenarios for prototypical three-dimensional gapless systems, such as a nodal-loop semimetal possessing SU(2) spin-rotational symmetry, and Dirac semimetals, transforming under (pseudo)spin-1/2 or 1 representations. The former system permits an unprecedented realization of a fourth-order phase, without any surface zero modes. Our construction can be generalized to HOT insulators and superconductors in any dimension and symmetry class.

  • 49.
    Cappelluti, Emmanuele
    et al.
    Istituto di Struttura della Materia, CNR (ISM-CNR), 34149 Trieste, Italy.
    Silva-Guillén, Jose Angel
    Instituto Madrileño de Estudios Avanzados, IMDEA Nanociencia, Calle Faraday 9, 28049 Madrid, Spain, Calle Faraday 9.
    Rostami, Habib
    Nordia SU; Department of Physics, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom, Claverton Down.
    Guinea, Francisco
    Instituto Madrileño de Estudios Avanzados, IMDEA Nanociencia, Calle Faraday 9, 28049 Madrid, Spain, Calle Faraday 9; Donostia International Physics Center, Paseo Manuel de Lardizábal 4, 20018 San Sebastián, Spain; Ikerbasque, Basque Foundation for Science, 48009 Bilbao, Spain.
    Flat-band optical phonons in twisted bilayer graphene2023Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, nr 12, artikel-id 125401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Twisting bilayer sheets of graphene have been proven to be an efficient way to manipulate the electronic Dirac-like properties, resulting in flat bands at magic angles. Inspired by the electronic model, we develop a continuum model for the lattice dynamics of twisted bilayer graphene and we show that a remarkable band flattening applies to almost all the high-frequency in-plane lattice vibration modes, including the valley Dirac phonon, valley optical phonon, and zone-center optical phonon bands. Utilizing an approximate approach, we estimate small but finite magic angles at which a vanishing phonon bandwidth is expected. In contrast to the electronic case, the existence of a restoring potential prohibits the emergence of a magic angle in a more accurate modeling. The predicted phonon band flattening is highly tunable by the twist angle and this strong dependence is directly accessible by spectroscopic tools.

  • 50.
    Cardias, Ramon
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. Instituto de Física, Universidade Federal Fluminense, 24210-346 Niterói, RJ, Brazil.
    Silva, Jhonatan dos Santos
    Faculdade de Física, Universidade Federal do Pará, 66075-110 Belém, PA, Brazil; Instituto Federal de Educação, Ciência e Tecnologia do Pará, 68250-000 Óbidos, PA, Brazil.
    Bergman, Anders
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden.
    Szilva, Attila
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden.
    Kvashnin, Yaroslav O.
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden.
    Fransson, Jonas
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden.
    Klautau, Angela B.
    Faculdade de Física, Universidade Federal do Pará, 66075-110 Belém, PA, Brazil; Departamento de Física da Universidade de Aveiro, 3810-183 Aveiro, Portugal.
    Eriksson, Olle
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden; Wallenberg Initiative Materials Science for Sustainability (WISE), Uppsala University Box 516, SE-75120 Uppsala, Sweden.
    Delin, Anna
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Material- och nanofysik. KTH, Centra, SeRC - Swedish e-Science Research Centre. Wallenberg Initiative Materials Science for Sustainability (WISE).
    Nordström, Lars
    Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden.
    Unraveling the connection between high-order magnetic interactions and local-to-global spin Hamiltonian in noncollinear magnetic dimers2023Ingår i: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, nr 22, artikel-id 224408Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A spin Hamiltonian that characterizes interatomic interactions between spin moments is highly valuable in predicting and comprehending the magnetic properties of materials. Here, we explore a method for explicitly calculating interatomic exchange interactions in noncollinear configurations of magnetic materials considering only a bilinear spin Hamiltonian in a local scenario. Based on density-functional theory calculations of dimers adsorbed on metallic surfaces, and with a focus on the Dzyaloshinskii-Moriya interaction (DMI) which is essential for stabilizing chiral noncollinear magnetic states, we discuss the interpretation of the DMI when decomposed into microscopic electron and spin densities and currents. We clarify the distinct origins of spin currents induced in the system and their connection to the DMI. In addition, we reveal how noncollinearity affects the usual DMI, which is solely induced by spin-orbit coupling, and DMI-like interactions brought about by noncollinearity. We explain how the dependence of the DMI on the magnetic configuration establishes a connection between high-order magnetic interactions, enabling the transition from a local to a global spin Hamiltonian.

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