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  • 201.
    Ntallis, Nikolaos
    et al.
    Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Borisov, Vladislav
    Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Kvashnin, Yaroslav O.
    Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Thonig, Danny
    Örebro Univ, Sch Sci & Technol, SE-70182 Örebro, Sweden..
    Sjoqvist, Erik
    Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Bergman, Anders
    Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Delin, Anna
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Applied Physics.
    Eriksson, Olle
    Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden.;Örebro Univ, Sch Sci & Technol, SE-70182 Örebro, Sweden..
    Pereiro, Manuel
    Uppsala Univ, Dept Phys & Astron, S-75120 Uppsala, Sweden..
    Connection between magnetic interactions and the spin-wave gap of the insulating phase of NaOsO32021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 13, article id 134433Article in journal (Refereed)
    Abstract [en]

    The scenario of a metal-insulator transition driven by the onset of antiferromagnetic order in NaOsO3 calls for a trustworthy derivation of the underlying effective spin Hamiltonian. To determine the latter we rely on ab initio electronic-structure calculations, linear spin-wave theory, and comparison to experimental data of the corresponding magnon spectrum. We arrive this way to Heisenberg couplings that are less than or similar to 45 to less than or similar to 63% smaller than values presently proposed in the literature and Dzyaloshinskii-Moriya interactions in the region of 15% of the Heisenberg exchange J. These couplings together with the symmetric anisotropic exchange interaction and single-ion magnetocrystalline anisotropy successfully reproduce the magnon dispersion obtained by resonant inelastic x-ray scattering measurements. In particular, the spin-wave gap fully agrees with the measured one. We find that the spin-wave gap is defined from a subtle interplay between the single-ion anisotropy, the Dzyaloshinskii-Moriya exchange, and the symmetric anisotropic exchange interactions. The results reported here underpin the local-moment description of NaOsO3, when it comes to analyzing the magnetic excitation spectra. Interestingly, this comes about from a microscopic theory that describes the electron system as Bloch states, adjusted to a mean-field solution to Hubbard-like interactions.

  • 202.
    Oestlin, A.
    et al.
    Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Theoret Phys 3, D-86135 Augsburg, Germany..
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Uppsala Univ, Dept Phys & Astron, Div Mat Theory, Box 516, SE-75120 Uppsala, Sweden.;Wigner Res Ctr Phys, Res Inst Solid State Phys & Opt, POB 49, H-1525 Budapest, Hungary..
    Chioncel, L.
    Univ Augsburg, Inst Phys, Ctr Elect Correlat & Magnetism, Theoret Phys 3, D-86135 Augsburg, Germany.;Univ Augsburg, Augsburg Ctr Innovat Technol, D-86135 Augsburg, Germany..
    Correlated electronic structure with uncorrelated disorder2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 23, article id 235135Article in journal (Refereed)
    Abstract [en]

    We introduce a computational scheme for calculating the electronic structure of random alloys that includes electronic correlations within the framework of the combined density functional and dynamical mean-field theory. By making use of the particularly simple parametrization of the electron Green's function within the linearized muffin-tin orbitals method, we show that it is possible to greatly simplify the embedding of the self-energy. This in turn facilitates the implementation of the coherent potential approximation, which is used to model the substitutional disorder. The computational technique is tested on the Cu-Pd binary alloy system, and for disordered Mn-Ni interchange in the half-metallic NiMnSb.

  • 203.
    Oestlin, A.
    et al.
    Univ Augsburg, Ctr Elect Correlat & Magnetism, Inst Phys, Theoret Phys 3, D-86135 Augsburg, Germany..
    Zhang, Y.
    Louisiana State Univ, Dept Phys & Astron, Baton Rouge, LA 70803 USA.;Louisiana State Univ, Ctr Computat & Technol, Baton Rouge, LA 70803 USA.;Kavli Inst Theoret Sci, Beijing 100190, Peoples R China..
    Terletska, H.
    Middle Tennessee State Univ, Dept Phys & Astron, Murfreesboro, TN 37132 USA..
    Beiuseanu, F.
    Univ Oradea, Fac Sci, RO-410087 Oradea, Romania..
    Popescu, V
    Sophie Scholl Gymnasium Oberhausen, D-46145 Oberhausen, Germany..
    Byczuk, K.
    Univ Warsaw, Fac Phys, Theoret Phys, Ul Pasteura 5, PL-02093 Warsaw, Poland..
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala Univ, Div Mat Theory, Dept Phys & Mat Sci, SE-75121 Uppsala, Sweden.;Hungarian Acad Sci, Res Inst Solid State Phys & Opt, POB 49, Budapest, Hungary..
    Jarrell, M.
    Louisiana State Univ, Dept Phys & Astron, Baton Rouge, LA 70803 USA.;Louisiana State Univ, Ctr Computat & Technol, Baton Rouge, LA 70803 USA..
    Vollhardt, D.
    Univ Augsburg, Ctr Elect Correlat & Magnetism, Inst Phys, Theoret Phys 3, D-86135 Augsburg, Germany..
    Chioncel, L.
    Univ Augsburg, Ctr Elect Correlat & Magnetism, Inst Phys, Theoret Phys 3, D-86135 Augsburg, Germany.;Univ Augsburg, Augsburg Ctr Innovat Technol, D-86135 Augsburg, Germany..
    Ab initio typical medium theory of substitutional disorder2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 1, article id 014210Article in journal (Refereed)
    Abstract [en]

    By merging single-site typical medium theory with density-functional theory, we introduce a self-consistent framework for electronic-structure calculations of materials with substitutional disorder which takes into account Anderson localization. The scheme and details of the implementation are presented and applied to the hypothetical alloy LicBe1-c, and the results are compared with those obtained with the coherent potential approximation. Furthermore, we demonstrate that Anderson localization suppresses ferromagnetic order for a very low concentration of (i) carbon impurities substituting oxygen in MgO1-cCc and (ii) manganese impurities substituting magnesium in Mg1-cMncO for the low-spin magnetic configuration.

  • 204.
    Olsen, V. S.
    et al.
    Univ Oslo, Ctr Mat Sci & Nanotechnol, Dept Phys, POB 1048, N-0316 Oslo, Norway..
    Baldissera, Gustavo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Zimmermann, C.
    Univ Oslo, Ctr Mat Sci & Nanotechnol, Dept Phys, POB 1048, N-0316 Oslo, Norway..
    Granerod, C. S.
    Univ Oslo, Ctr Mat Sci & Nanotechnol, Dept Phys, POB 1048, N-0316 Oslo, Norway..
    Bazioti, C.
    Univ Oslo, Ctr Mat Sci & Nanotechnol, Dept Phys, POB 1048, N-0316 Oslo, Norway..
    Galeckas, A.
    Univ Oslo, Ctr Mat Sci & Nanotechnol, Dept Phys, POB 1048, N-0316 Oslo, Norway..
    Svensson, B. G.
    Univ Oslo, Ctr Mat Sci & Nanotechnol, Dept Phys, POB 1048, N-0316 Oslo, Norway..
    Kuznetsov, A. Yu
    Univ Oslo, Ctr Mat Sci & Nanotechnol, Dept Phys, POB 1048, N-0316 Oslo, Norway..
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Univ Oslo, Ctr Mat Sci & Nanotechnol, Dept Phys, POB 1048, N-0316 Oslo, Norway..
    Prytz, O.
    Univ Oslo, Ctr Mat Sci & Nanotechnol, Dept Phys, POB 1048, N-0316 Oslo, Norway..
    Vines, L.
    Univ Oslo, Ctr Mat Sci & Nanotechnol, Dept Phys, POB 1048, N-0316 Oslo, Norway..
    Evidence of defect band mechanism responsible for band gap evolution in (ZnO)(1-x)(GaN)(x) alloys2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 16, article id 165201Article in journal (Refereed)
    Abstract [en]

    It is known that (ZnO)(1-x)(GaN)(x) alloys demonstrate remarkable energy band bowing, making the material absorb in the visible range, in spite of the binary components being classical wide band gap semiconductors. However, the origin of this bowing is not settled; two major mechanisms are under debate: Influence of the orbital repulsion and/or formation of a defect band. In the present work, we applied a combination of the absorption and emission measurements on the samples exhibiting an outstanding nanoscale level of (ZnO)(1-x)(GaN)(x) homogeneity as monitored by the high resolution electron microscopy equipped with the energy dispersive x-ray analysis and the electron energy loss spectroscopy; moreover the experimental data were set in the context of the computational analysis of the alloys employing density functional theory and quasiparticle GW approximation. A prominent discrepancy in the band gap values as deduced from the absorption and emission experiments was observed systematically for the alloys with different compositions and interpreted as evidence for the absorption gap shrinking due to the defect band formation. Computational data support the argument, revealing only minor variations in the bulk of the conduction and valence band structures of the alloys, except for a characteristic "tail" in the vicinity of the valence band maximum. As such, we conclude that the energy gap bowing in (ZnO)(1-x)(GaN)(x) alloys is due to the defect band formation, presumably at the top of the valence band maximum.

  • 205.
    Olsthoorn, Bart
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Hannes Alfvens Vag 12, SE-10691 Stockholm, Sweden..
    Persistent homology of quantum entanglement2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 11, article id 115174Article in journal (Refereed)
    Abstract [en]

    Structure in quantum entanglement entropy is often leveraged to focus on a small corner of the exponentially large Hilbert space and efficiently parametrize the problem of finding ground states. A typical example is the use of matrix product states for local and gapped Hamiltonians. We study the structure of entanglement entropy using persistent homology, a relatively new method from the field of topological data analysis. The inverse quantum mutual information between pairs of sites is used as a distance metric to form a filtered simplicial complex. Both ground states and excited states of common spin models are analyzed as an example. Furthermore, the effect of homology with different coefficients and boundary conditions is also explored. Beyond these basic examples, we also discuss the promising future applications of this modern computational approach, including its connection to the question of how space-time could emerge from entanglement.

  • 206.
    Olsthoorn, Bart
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Mass fluctuations and absorption rates in dark-matter sensors based on Dirac materials2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 4, article id 045120Article in journal (Refereed)
    Abstract [en]

    We study the mass fluctuations in gapped Dirac materials by treating the mass term as both a continuous and discrete random variable. Gapped Dirac materials were proposed to be used as materials for dark-matter sensors. One thus would need to estimate the role of disorder and fluctuations on the interband absorption of dark matter. We find that both continuous and discrete fluctuations across the sample introduce tails (e.g., Dirac-Lifshitz tails) in the density of states and the interband absorption rate. We estimate the strength of the gap filling and discuss implications of these fluctuations on the performance as sensors for dark matter detection. The approach used in this work provides a basic framework to model the disorder by any arbitrary mechanism on the interband absorption of Dirac material sensors.

  • 207.
    Ortega-Taberner, Carlos
    et al.
    Nordita SU; Stockholm Univ, Stockholm, Sweden..
    Hermanns, Maria
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Stockholm, Sweden..
    From Hermitian critical to non-Hermitian point-gapped phases2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 23, article id 235112Article in journal (Refereed)
    Abstract [en]

    Recent years have seen a growing interest in topological phases beyond the standard paradigm of gapped isolated systems. One recent direction is to explore topological features in non-Hermitian systems that are commonly used as effective descriptions of open systems. Another direction explores the fate of topology at critical points, where the bulk gap collapses. One interesting observation is that both systems, though very different, share certain topological features. For instance, both systems can host half-integer quantized winding numbers and have very similar entanglement spectra. Here we make this similarity explicit by showing the equivalence of topological invariants in critical systems with non-Hermitian point-gap phases, in the presence of sublattice symmetry. Also, the corresponding entanglement spectra show the same topological features. This correspondence may carry over to other features and even be helpful to deepen our understanding of non-Hermitian systems using our knowledge of critical systems and vice versa.

  • 208.
    Ortega-Taberner, Carlos
    et al.
    Stockholm Univ, AlbaNova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden.;KTH Royal Inst Technol, Nordita, SE-10691 Stockholm, Sweden.;Stockholm Univ, SE-10691 Stockholm, Sweden..
    Hermanns, Maria
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, AlbaNova Univ Ctr, Dept Phys, SE-10691 Stockholm.
    Relation of the entanglement spectrum to the bulk polarization2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, no 19, article id 195132Article in journal (Refereed)
    Abstract [en]

    The bulk polarization is a Z(2) topological invariant characterizing noninteracting systems in one dimension with chiral or particle-hole symmetries. We show that the bulk polarization can always be determined from the single-particle entanglement spectrum, even in the absence of symmetries that quantize it. In the symmetric case, the known relation between the bulk polarization and the number of virtual topological edge modes is recovered. We use the bulk polarization to compute Chern numbers in one and two dimensions, which illuminates their known relation to the entanglement spectrum. Furthermore, we discuss an alternative bulk polarization that can carry more information about the surface spectrum than the conventional one and can simplify the calculation of Chern numbers.

  • 209.
    Ortega-Taberner, Carlos
    et al.
    Stockholm Univ, AlbaNova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden.;Nordita SU.
    Jauho, Antti-Pekka
    Tech Univ Denmark, Ctr Nanostruct Graphene, Dept Phys, DK-2800 Kongens Lyngby, Denmark..
    Paaske, Jens
    Univ Copenhagen, Niels Bohr Inst, Ctr Quantum Devices, DK-2100 Copenhagen, Denmark..
    Anomalous Josephson current through a driven double quantum dot2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 11, article id 115165Article in journal (Refereed)
    Abstract [en]

    Josephson junctions based on quantum dots offer a convenient tunability by means of local gates. Here we analyze a Josephson junction based on a serial double quantum dot in which the two dots are individually gated by phase-shifted microwave tones of equal frequency. We calculate the time-averaged current across the junction and determine how the phase shift between the drives modifies the current-phase relation of the junction. Breaking particle-hole symmetry on the dots is found to give rise to a finite average anomalous Josephson current with phase bias between the superconductors fixed to zero. This microwave gated weak link thus realizes a tunable "Floquet v0 junction" with maximum critical current achieved for driving frequencies slightly off resonance with the subgap excitation energy. We provide numerical results supported by an analytical analysis for infinite superconducting gap and weak interdot coupling. We identify an interaction-driven 0-ir transition of anomalous Josephson current as a function of driving phase difference. Finally, we show that this junction can be tuned so as to provide for complete rectification of the time-averaged Josephson current-phase relation.

  • 210.
    Ortega-Taberner, Carlos
    et al.
    Stockholm Univ, Dept Phys, AlbaNova Univ Ctr, SE-10691 Stockholm, Sweden.; NORDITA SU.
    Rodland, Lukas
    Stockholm Univ, Dept Phys, AlbaNova Univ Ctr, SE-10691 Stockholm, Sweden..
    Hermanns, Maria
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Dept Phys, AlbaNova Univ Ctr, SE-10691 Stockholm, Sweden..
    Polarization and entanglement spectrum in non-Hermitian systems2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 7, article id 075103Article in journal (Refereed)
    Abstract [en]

    The entanglement spectrum is a useful tool to study topological phases of matter, and contains valuable information about the ground state of the system. Here, we study its properties for free non-Hermitian systems for both point-gapped and line-gapped phases. While the entanglement spectrum only retains part of the topological information in the former case, it is very similar to Hermitian systems in the latter. In particular, it not only mimics the topological edge modes, but also contains all the information about the polarization, even in systems that are not topological. Furthermore, we show that the Wilson loop is equivalent to the many-body polarization and that it reproduces the phase diagram for the system with open boundaries, despite being computed for a periodic system.

  • 211. Ostlin, A.
    et al.
    Vitos, Levente
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics. Department of Physics and Astronomy, Division of Materials Theory, Uppsala University, Box 516, SE-75120 Uppsala, Sweden; Research Institute for Solid State Physics and Optics, Wigner Research Center for Physics, P.O. Box 49, H-1525 Budapest, Hungary.
    Chioncel, L.
    Analytic continuation-free Green's function approach to correlated electronic structure calculations2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 12, article id 125156Article in journal (Refereed)
    Abstract [en]

    We present a charge self-consistent scheme combining density functional and dynamical mean field theory, which uses Green's functions of multiple-scattering type. In this implementation, the many-body effects are incorporated into the Kohn-Sham iterative scheme without the need for the numerically ill-posed analytic continuation of the Green's function and of the self-energy, which was previously a bottleneck in multiple-scattering-type Green's function approaches. This is achieved by producing the Kohn-Sham Hamiltonian in the subspace of correlated partial waves and allows to formulate the Green's function directly on theMatsubara axis. The spectral moments of the Matsubara Green's function enable us to put together the real-space charge density, therefore, the charge self-consistency can be achieved. Our results for the spectral functions (density of states) and equation-of-state curves for transition-metal elements Fe, Ni, and FeAl compound agree very well with those of Hamiltonian-based LDA+DMFT implementations. The current implementation improves on numerical accuracy, compared to previous implementations where analytic continuation was required at each Kohn-Sham self-consistent step. A minimal effort aside from the multiple-scattering formulation is required, and the method can be generalized in several ways that are interesting for applications to real materials.

  • 212.
    Pan, Fan
    et al.
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Applied Physics.
    Chico, Jonathan
    Delin, Anna
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Applied Physics. Uppsala Univ, Sweden.
    Bergman, Anders
    Bergqvist, Lars
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Applied Physics.
    Extended spin model in atomistic simulations of alloys2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 18, article id 184432Article in journal (Refereed)
    Abstract [en]

    An extended atomistic spin model allowing for studies of the finite-temperature magnetic properties of alloys is proposed. The model is obtained by extending the Heisenberg Hamiltonian via a parametrization from a first-principles basis, interpolating from both the low-temperature ferromagnetic and the high-temperature paramagnetic reference states. This allows us to treat magnetic systems with varying degree of itinerant character within the model. Satisfactory agreement with both previous theoretical studies and experiments are obtained in terms of Curie temperatures and paramagnetic properties. The proposed model is not restricted to elements but is also applied to binary alloys, such as the technologically important material permalloy, where significant differences in the finite magnetic properties of Fe and Ni magnetic moments are found. The proposed model strives to find the right compromise between accuracy and computational feasibility for accurate modeling, even for complex magnetic alloys and compounds.

  • 213.
    Pan, Fan
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Chico, Jonathan
    Hellsvik, Johan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Delin, Anna
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre. Uppsala University, Sweden.
    Bergman, Anders
    Bergqvist, Lars
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Systematic study of magnetodynamic properties at finite temperatures in doped permalloy from first-principles calculations2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 21, article id 214410Article in journal (Refereed)
    Abstract [en]

    By means of first-principles calculations, we have systematically investigated how the magnetodynamic properties Gilbert damping, magnetization, and exchange stiffness are affected when permalloy (Py) (Fe0.19Ni0.81) is doped with 4d or 5d transition metal impurities. We find that the trends in the Gilbert damping can be understood from relatively few basic parameters such as the density of states at the Fermi level, the spin-orbit coupling, and the impurity concentration. The temperature dependence of the Gilbert damping is found to be very weak which we relate to the lack of intraband transitions in alloys. Doping with 4d elements has no major impact on the studied Gilbert damping, apart from diluting the host. However, the 5d elements have a profound effect on the damping and allow it to be tuned over a large interval while maintaining the magnetization and exchange stiffness. As regards the spin stiffness, doping with early transition metals results in considerable softening, whereas late transition metals have a minor impact. Our result agree well with earlier calculations where available. In comparison to experiments, the computed Gilbert damping appears slightly underestimated, whereas the spin stiffness shows a general good agreement.

  • 214.
    Pankratova, M.
    et al.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Miranda, I. P.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Thonig, D.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Örebro Univ, Sch Sci & Technol, SE-70182 Örebro, Sweden..
    Pereiro, M.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Sjoqvist, E.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Delin, Anna
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Applied Physics.
    Eriksson, O.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Örebro Univ, Sch Sci & Technol, SE-70182 Örebro, Sweden..
    Bergman, A.
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Heat-conserving three-temperature model for ultrafast demagnetization in nickel2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, no 17Article in journal (Refereed)
    Abstract [en]

    Multireservoir models are widely used for modeling and interpreting ultrafast magnetization dynamics. Here we introduce an alternative formulation to existing three-temperature models for the treatment of spin, electron, and lattice temperatures in magnetization dynamics simulations. In contrast to most existing models of calculations of energy transfer between reservoirs in these types of simulations, the heat distribution of the spin and lattice subsystems is evaluated during the simulation instead of being calculated a priori. The model is applied to investigate the demagnetization and remagnetization of fcc Ni, when subjected to a strong laser pulse. In particular, our model results in a fast interplay between the electron and spin subsystems which reproduces the main features of experimental data for fcc Ni significantly better than most reported three-temperature models. We also show that the way in which the electron, spin, and lattice heat capacities are described can have a significant impact on the simulated ultrafast dynamics. By introducing spin-lattice couplings in the simulation, it is shown that these explicit interactions only have a marginal impact on the magnetization dynamics of fcc Ni, albeit it is more pronounced for higher laser pulse powers.

  • 215.
    Papadopoulos, Konstantinos
    et al.
    Chalmers Univ Technol, Dept Phys, S-41296 Gothenburg, Sweden..
    Forslund, Ola Kenji
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Chalmers Univ Technol, Dept Phys, S-41296 Gothenburg, Sweden..
    Nocerino, Elisabetta
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Johansson, Fredrik
    KTH, School of Engineering Sciences (SCI), Applied Physics. Uppsala Univ, Div Mol & Condensed Matter Phys, S-75237 Uppsala, Sweden.;Sorbonne Univ, Inst Nanosci Paris, UMR CNRS 7588, F-75005 Paris, France..
    Simutis, Gediminas
    Chalmers Univ Technol, Dept Phys, S-41296 Gothenburg, Sweden.;Paul Scherrer Inst, Lab Neutron & Muon Instrumentat, CH-5232 Villigen, Switzerland..
    Matsubara, Nami
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Morris, Gerald
    TRIUMF, 4004 Wesbrook Mall, Vancouver, BC 623, Canada..
    Hitti, Bassam
    TRIUMF, 4004 Wesbrook Mall, Vancouver, BC 623, Canada..
    Arseneau, Donald
    TRIUMF, 4004 Wesbrook Mall, Vancouver, BC 623, Canada..
    Svedlindh, Peter
    Uppsala Univ, Dept Mat Sci & Engn, S-75103 Uppsala, Sweden..
    Medarde, Marisa
    Paul Scherrer Inst, Lab Multiscale Mat Expt, CH-5232 Villigen, Switzerland..
    Andreica, Daniel
    Babes Bolyai Univ, Fac Phys, Cluj Napoca 400084, Cluj, Romania..
    Orain, Jean-Christophe
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Pomjakushin, Vladimir
    Paul Scherrer Inst, Lab Neutron Scattering & Imaging, CH-5232 Villigen, Switzerland..
    Börjesson, Lars
    Chalmers Univ Technol, Dept Phys, S-41296 Gothenburg, Sweden..
    Sugiyama, Jun
    Uppsala Univ, Div Mol & Condensed Matter Phys, S-75237 Uppsala, Sweden.;Comprehens Res Org Sci & Soc CROSS, Neutron Sci & Technol Ctr, Tokai, Ibaraki 3191106, Japan..
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Sassa, Yasmine
    Chalmers Univ Technol, Dept Phys, S-41296 Gothenburg, Sweden..
    Influence of the magnetic sublattices in the double perovskite LaCaNiReO62022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, no 21, article id 214410Article in journal (Refereed)
    Abstract [en]

    The magnetism of double perovskites is a complex phenomenon, determined from intra- or interatomic magnetic moment interactions, and strongly influenced by geometry. We take advantage of the complementary length and timescales of the muon spin rotation, relaxation, and resonance (mu+SR) microscopic technique and bulk ac/dc magnetic susceptibility measurements to study the magnetic phases of the LaCaNiReO6 double perovskite. As a result, we are able to discern and report ferrimagnetic ordering below TC = 102 K and the formation of different magnetic domains above TC. Between TC < T < 270 K, the following two magnetic environments appear, a dense spin region and a static-dilute spin region. The paramagnetic state is obtained only above T > 270 K. An evolution of the interaction between Ni and Re magnetic sublattices, in this geometrically frustrated fcc perovskite structure, is revealed as a function of temperature through the critical behavior and thermal evolution of microscopic and macroscopic physical quantities.

  • 216. Paul, S.
    et al.
    Iuşan, D.
    Thunström, P.
    Kvashnin, Y. O.
    Hellsvik, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Pereiro, M.
    Delin, Anna
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Knut, R.
    Phuyal, D.
    Lindblad, A.
    Karis, O.
    Sanyal, B.
    Eriksson, O.
    Investigation of the spectral properties and magnetism of BiFeO3 by dynamical mean-field theory2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 12, article id 125120Article in journal (Refereed)
    Abstract [en]

    Using the local density approximation plus dynamical mean-field theory (LDA+DMFT), we have computed the valence-band photoelectron spectra and magnetic excitation spectra of BiFeO3, one of the most studied multiferroics. Within the DMFT approach, the local impurity problem is tackled by the exact diagonalization solver. The solution of the impurity problem within the LDA+DMFT method for the paramagnetic and magnetically ordered phases produces result in agreement with the experimental data on electronic and magnetic structures. For comparison, we also present results obtained by the LDA+U approach which is commonly used to compute the physical properties of this compound. Our LDA+DMFT derived electronic spectra match adequately with the experimental hard x-ray photoelectron spectroscopy and resonant photoelectron spectroscopy for Fe 3d states, whereas the LDA+U method fails to capture the general features of the measured spectra. This indicates the importance of accurately incorporating the dynamical aspect of electronic correlation among Fe 3d orbitals to reproduce the experimental excitation spectra. Specifically, the LDA+DMFT derived density of states exhibits a significant amount of Fe 3d states at the position of Bi lone pairs, implying that the latter are not alone in the spectral scenario. This fact might modify our interpretation about the origin of ferroelectric polarization in this material. Our study demonstrates that the combination of orbital cross sections for the constituent elements and broadening schemes for the spectral functions are crucial to explain the detailed structures of the experimental electronic spectra. Our magnetic excitation spectra computed from the LDA+DMFT result conform well with the inelastic neutron scattering data.

  • 217.
    Peng, Bo
    et al.
    Univ Cambridge, Cavendish Lab, TCM Grp, JJ Thomson Ave, Cambridge CB3 0HE, England..
    Bouhon, Adrien
    Stockholm Univ, Nordita SU, Hannes Alfvens Vag 12, SE-10691 Stockholm, Sweden..
    Slager, Robert-Jan
    Univ Cambridge, Cavendish Lab, TCM Grp, JJ Thomson Ave, Cambridge CB3 0HE, England..
    Monserrat, Bartomeu
    Univ Cambridge, Cavendish Lab, TCM Grp, JJ Thomson Ave, Cambridge CB3 0HE, England.;Univ Cambridge, Dept Mat Sci & Met, 27 Charles Babbage Rd, Cambridge CB3 0FS, England..
    Multigap topology and non-Abelian braiding of phonons from first principles2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 8, article id 085115Article in journal (Refereed)
    Abstract [en]

    Non-Abelian states of matter, in which the final state depends on the order of the interchanges of two quasipar-ticles, can encode information immune from environmental noise with the potential to provide a robust platform for topological quantum computation. We demonstrate that phonons can carry non-Abelian frame charges at the band-crossing points of their frequency spectrum, and that external stimuli can drive their braiding. We present a general framework to understand the topological configurations of phonons from first-principles calculations using a topological invariant called Euler class, and provide a complete analysis of phonon braiding by combining different topological configurations. Taking a well-known dielectric material Al2O3 as a representative example, we demonstrate that electrostatic doping gives rise to phonon band inversions that can induce redistribution of the frame charges, leading to non-Abelian braiding of phonons. Our work provides a quasiparticle platform for realizable non-Abelian braiding in reciprocal space, and expands the tool set for studying braiding processes.

  • 218.
    Pertsova, Anna
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Linnæus University, Sweden.
    Canali, C. M.
    MacDonald, A. H.
    Quantum Hall edge states in topological insulator nanoribbons2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 12, article id 121409Article in journal (Refereed)
    Abstract [en]

    We present a microscopic theory of the chiral one-dimensional electron gas system localized on the sidewalls of magnetically doped Bi2Se3-family topological insulator nanoribbons in the quantum anomalous Hall effect (QAHE) regime. Our theory is based on a simple continuum model of sidewall states whose parameters are extracted from detailed ribbon and film geometry tight-binding model calculations. In contrast to the familiar case of the quantum Hall effect in semiconductor quantum wells, the number of microscopic chiral channels depends simply and systematically on the ribbon thickness and on the position of the Fermi level within the surface state gap. We use our theory to interpret recent transport experiments that exhibit nonzero longitudinal resistance in samples with accurately quantized Hall conductances.

  • 219.
    Pertsova, Anna
    et al.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Geilhufe, Matthias
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Bremholm, Martin
    Aarhus Univ, Dept Chem, DK-8000 Aarhus, Denmark.;Aarhus Univ, iNANO, DK-8000 Aarhus, Denmark.;Aarhus Univ, Ctr Mat Crystallog, DK-8000 Aarhus, Denmark..
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Computational search for Dirac and Weyl nodes in f-electron antiperovskites2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 20, article id 205126Article in journal (Refereed)
    Abstract [en]

    We present the result of an ab initio search for new Dirac materials among inverse perovskites. Our investigation is focused on the less studied class of lanthanide antiperovskites containing heavy f-electron elements in the cation position. Some of the studied compounds have not yet been synthesized experimentally. Our computational approach is based on density functional theory calculations which account for spin-orbit interaction and strong correlations of the f-electron atoms. We find several promising candidates among lanthanide antiperovskites which host bulk Dirac states close to the Fermi level. Specifically, our calculations reveal massive three-dimensional Dirac states in materials of the class A(3)BO, where A=Sm, Eu, Gd, Yb, and B=Sn, Pb. In materials with finite magnetic moment, such as Eu3BO (B=Sn, Pb), the degeneracy of the Dirac nodes is lifted, leading to appearance of Weyl nodes.

  • 220.
    Pinon, Sarah
    et al.
    Univ Paris Saclay, Inst Phys Theor, CEA, CNRS,Orme Merisiers, F-91190 Gif Sur Yvette, France..
    Kaladzhyan, Vardan
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Bena, Cristina
    Univ Paris Saclay, Inst Phys Theor, CEA, CNRS,Orme Merisiers, F-91190 Gif Sur Yvette, France..
    Modeling long imperfect SNS junctions and Andreev bound states using two impurities and the T-matrix formalism2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 20, article id 205136Article in journal (Refereed)
    Abstract [en]

    We provide an analytical tool to calculate the energies of Andreev bound states (ABSs) in long imperfect SNS junctions, which at present can only be described using numerical tools. We model an NS junction as a delta-function "Andreev" impurity, i.e., a localized potential that scatters an electron into a hole with opposite spin. We show using the scattering matrix formalism that, quite surprisingly, an "Andreev" impurity is equivalent to an NS junction characterized by both Andreev reflection and a finite amount of normal scattering. The ABS energies are then calculated using the T-matrix formalism applied to a system with two Andreev impurities. Our results lie between those for a perfect long SNS junction limit described by the Andreev approximation (ABS energies depend linearly on the phase and are independent of the chemical potential) and the particle-in-the-box limit (bound state energies are independent of the phase and have a linear dependence on the chemical potential). Moreover, we recover a closed-form expression for the ABS energies by expanding around the particle-in-the-box limit.

  • 221.
    Pinon, Sarah
    et al.
    Univ Paris Saclay, Inst Phys Theor, CEA, CNRS,Orme Merisiers, F-91190 Gif Sur Yvette, France..
    Kaladzhyan, Vardan
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Bena, Cristina
    Univ Paris Saclay, Inst Phys Theor, CEA, CNRS,Orme Merisiers, F-91190 Gif Sur Yvette, France..
    Surface Green's functions and boundary modes using impurities: Weyl semimetals and topological insulators2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 11, article id 115405Article in journal (Refereed)
    Abstract [en]

    In this work we provide a direct and non-numerical technique to obtain the surface Green's functions for three-dimensional systems. This technique is based on the ideas presented by V. Kaladzhyan and C. Bena [Phys. Rev. B 100, 081106(R) (2019)], in which we start with an infinite system and model the boundary using a planelike infinite-amplitude potential. Such a configuration can be solved exactly using the T-matrix formalism. We apply our method to calculate the surface Green's function and the corresponding Fermi-arc states for Weyl semimetals. We also apply the technique to systems of lower dimensions, such as Kane-Mele and Chern insulator models, to provide a more efficient and non-numerical method to describe the formation of edge states.

  • 222.
    Pinon, Sarah
    et al.
    Univ Paris Saclay, Inst Phys Theor, Orme Merisiers, CEA CNRS, F-91190 Gif Sur Yvette, France..
    Kaladzhyan, Vardan
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Bena, Cristina
    Univ Paris Saclay, Inst Phys Theor, Orme Merisiers, CEA CNRS, F-91190 Gif Sur Yvette, France..
    Surface Green's functions and quasiparticle interference in Weyl semimetals2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, no 16, article id 165117Article in journal (Refereed)
    Abstract [en]

    We use the exact analytical technique introduced by us [Phys. Rev. B 101, 115405 (2020)] to recover the surface Green's functions and the corresponding Fermi-arc surface states for various lattice models of Weyl semimetals. For these models we use the T-matrix formalism to calculate the quasiparticle interference patterns generated in the presence of impurity scattering. In particular, we consider the models introduced by Kourtis et al. [Phys. Rev. B 93, 041109(R) (2016)] (model A) and Lau et al. [Phys. Rev. Lett. 119, 076801 (2017)] (model B), and we find that, as opposed to observations previously obtained via joint density of states and spin-dependent scattering probability, the interarc scattering in the quasiparticle interference features is fully suppressed in model A, and is very small in model B. Our findings indicate that these models may not correctly describe materials such as MoTe2, since for such materials interarc scattering is clearly visible experimentally, e.g., by Deng et al. [Nat. Phys. 12, 1105 (2016)]. We also focus on the minimal models proposed by McCormick et al. [Phys. Rev. B 95, 075133 (2017)], which indeed recover significant interarc scattering features.

  • 223.
    Pogoryelov, Yevgen
    et al.
    Uppsala Univ, Dept Phys & Astron, S-75121 Uppsala, Sweden..
    Pereiro, Manuel
    Uppsala Univ, Dept Phys & Astron, S-75121 Uppsala, Sweden..
    Jana, Somnath
    Uppsala Univ, Dept Phys & Astron, S-75121 Uppsala, Sweden..
    Kumar, Ankit
    Uppsala Univ, Dept Engn Sci, S-75121 Uppsala, Sweden..
    Akansel, Serkan
    Uppsala Univ, Dept Engn Sci, S-75121 Uppsala, Sweden..
    Ranjbar, Mojtaba
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Thonig, Danny
    Orebro Univ, Sch Sci & Technol, S-70182 Orebro, Sweden..
    Primetzhofer, Daniel
    Uppsala Univ, Dept Phys & Astron, S-75121 Uppsala, Sweden..
    Svedlindh, Peter
    Uppsala Univ, Dept Engn Sci, S-75121 Uppsala, Sweden..
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics. Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Eriksson, Olle
    Uppsala Univ, Dept Phys & Astron, S-75121 Uppsala, Sweden.;Orebro Univ, Sch Sci & Technol, S-70182 Orebro, Sweden..
    Karis, Olof
    Uppsala Univ, Dept Phys & Astron, S-75121 Uppsala, Sweden..
    Arena, Dario A.
    Univ S Florida, Dept Phys, Tampa, FL 33620 USA..
    Nonreciprocal spin pumping damping in asymmetric magnetic trilayers2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 5, article id 054401Article in journal (Refereed)
    Abstract [en]

    In magnetic trilayer systems, spin pumping is generally addressed as a reciprocal mechanism characterized by one unique spin-mixing conductance common to both interfaces. However, this assumption is questionable in cases where different types of interfaces are present. Here, we present a general theory for analyzing spin pumping in cases with more than one unique interface and where the magnetic coupling is allowed to be noncollinear. The theory is applied to analyze layer-resolved ferromagnetic resonance experiments on the trilayer system Ni80Fe20/Ru/Fe49Co49V2 where the Ru spacer thickness is varied to tune the indirect exchange coupling. It is demonstrated that the equation of motion of macrospins driven by spin pumping need to be modified in case of noncollinear coupling. Our analysis also shows that the spin pumping in trilayer systems with dissimilar magnetic layers, in general, is nonreciprocal.

  • 224.
    Polishchuk, Dmytr
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. Institute of Magnetism of the NAS of Ukraine and MES of Ukraine, 03142 Kyiv, Ukraine.
    Tykhonenko Polishchuk, Yuliya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. Institute of Magnetism of the NAS of Ukraine and MES of Ukraine, 03142 Kyiv, Ukraine.
    Lytvynenko, Ya M.
    Institute of Magnetism of the NAS of Ukraine and MES of Ukraine, 03142 Kyiv, Ukraine; Institut für Physik, Johannes Gutenberg Universität Mainz, D-55128 Mainz, Germany.
    Rostas, A. M.
    National Institute of Materials Physics, 077125 Bucharest-Magurele, Romania, Magurele.
    Kuncser, V.
    National Institute of Materials Physics, 077125 Bucharest-Magurele, Romania, Magurele.
    Kravets, Anatolii
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. Institute of Magnetism of the NAS of Ukraine and MES of Ukraine, 03142 Kyiv, Ukraine.
    Tovstolytkin, A. I.
    Institute of Magnetism of the NAS of Ukraine and MES of Ukraine, 03142 Kyiv, Ukraine; Faculty of Radiophysics, Electronics and Computer Systems, Taras Shevchenko National University of Kyiv, 64/13 Volodymyrska Str., 01601 Kyiv, Ukraine, 64/13 Volodymyrska Str..
    Gomonay, O. V.
    Institut für Physik, Johannes Gutenberg Universität Mainz, D-55128 Mainz, Germany.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Antiferromagnet-mediated interlayer exchange: Hybridization versus proximity effect2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 22, article id 224432Article in journal (Refereed)
    Abstract [en]

    We investigate the interlayer coupling between two thin ferromagnetic (F) films mediated by an antiferromagnetic (AF) spacer in F∗/AF/F trilayers and show how it transitions between different regimes on changing the AF thickness. Employing layer-selective Kerr magnetometry and ferromagnetic-resonance techniques in a complementary manner enables us to distinguish between three functionally distinct regimes of such ferromagnetic interlayer coupling. The F layers are found to be individually and independently exchange-biased for thick FeMn spacers - the first regime of no interlayer F-F∗ coupling. F-F∗ coupling appears on decreasing the FeMn thickness below 9 nm. In this second regime found in structures with 6.0-9.0-nm-thick FeMn spacers, the interlayer coupling exists only in a finite temperature interval just below the effective Néel temperature of the spacer, which is due to magnon-mediated exchange through the thermally softened antiferromagnetic spacer, vanishing at lower temperatures. The third regime, with FeMn thinner than 4 nm, is characterized by a much stronger interlayer coupling in the entire temperature interval, which is attributed to a magnetic-proximity induced ferromagnetic exchange. These experimental results, spanning the key geometrical parameters and thermal regimes of the F∗/AF/F nanostructure, complemented by a comprehensive theoretical analysis, should broaden the understanding of the interlayer exchange in magnetic multilayers and potentially be useful for applications in spin thermionics.

  • 225.
    Polishchuk, Dmytr
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Tykhonenko-Polishchuk, Yuliya
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. National Academy of Sciences of Ukraine, Ukraine.
    Holmgren, Erik
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Kravets, Anatolii
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. National Academy of Sciences of Ukraine, Ukraine.
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Thermally induced antiferromagnetic exchange in magnetic multilayers2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 10, article id 104427Article in journal (Refereed)
    Abstract [en]

    We demonstrate sharp thermally induced switching between ferromagnetic and antiferromagnetic RKKY ( Ruderman-Kittel-Kasuya-Yosida) exchange in a spin-valve with the spacer incorporating a thin diluted ferromagnetic layer as the core. We illustrate the mechanism behind the effect as being due to a change in the effective thickness of the spacer induced by the Curie transition into its paramagnetic state. The ability to switch between ferromagnetic and antiferromagnetic states in a magnetic multilayer by a slight change in temperature may lead to new types of spin-thermoelectronic devices for use in such applications as memory or oscillators.

  • 226.
    Polishchuk, Dmytro M.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. NAS Ukraine, Inst Magnetism, UA-03680 Kiev, Ukraine..
    Polek, T. , I
    Kamra, A.
    Norwegian Univ Sci & Technol, Ctr Quantum Spintron, Dept Phys, NO-7491 Trondheim, Norway..
    Kravets, Anatolii
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics. NAS Ukraine, Inst Magnetism, UA-03680 Kiev, Ukraine..
    Tovstolytkin, A. , I
    Brataas, A.
    Norwegian Univ Sci & Technol, Ctr Quantum Spintron, Dept Phys, NO-7491 Trondheim, Norway..
    Korenivski, Vladislav
    KTH, School of Engineering Sciences (SCI), Applied Physics, Nanostructure Physics.
    Spin relaxation in multilayers with synthetic ferrimagnets2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 14, article id 144401Article in journal (Refereed)
    Abstract [en]

    We demonstrate the strong tunability of the spin-pumping contribution to magnetic damping in a thin-film ferromagnetic free layer interfacing with a synthetic ferrimagnet (SFM), acting as a spin sink, via a thin Cu spacer. The effect strongly depends on the magnetic state of the SFM, a trilayer structure composed of two Fe layers coupled via indirect exchange mediated by a Cr spacer. With increasing Cr thickness, the SFM state undergoes a transition from an antiparallel configuration via a noncollinear configuration to a parallel configuration. We can explain the corresponding nonmonotonous dependence of spin relaxation in the free layer in terms of modulation of the longitudinal spin transport as well as relaxation of the transverse angular momentum in the SFM. The results should be useful for designing high-speed spintronic devices where tunability of spin relaxation is advantageous.

  • 227. Polyakov, A.
    et al.
    Tusche, C.
    Ellguth, M.
    Crozier, E. D.
    Mohseni, K.
    Otrokov, M. M.
    Zubizarreta, X.
    Vergniory, M. G.
    Geilhufe, Matthias
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Max-Planck-Institut für Mikrostrukturphysik, Germany.
    Chulkov, E. V.
    Ernst, A.
    Meyerheim, H. L.
    Parkin, S. S. P.
    Instability of the topological surface state in Bi2Se3 upon deposition of gold2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 18, article id 180202Article in journal (Refereed)
    Abstract [en]

    Momentum-resolved photoemission spectroscopy indicates the instability of the Dirac surface state upon deposition of gold on the (0001) surface of the topological insulator Bi2Se3. Based on the structure model derived from extended x-ray absorption fine structure experiments showing that gold atoms substitute bismuth atoms, first-principles calculations provide evidence that a gap appears due to hybridization of the surface state with gold d states near the Fermi level. Our findings provide insights into the mechanisms affecting the stability of the surface state.

  • 228.
    Polyakov, A.
    et al.
    Max Planck Inst Mikrostrukturphys, Weinberg 2, D-06120 Halle, Germany..
    Tusche, C.
    Max Planck Inst Mikrostrukturphys, Weinberg 2, D-06120 Halle, Germany.;Forschungszentrum Julich, Peter Grunberg Inst PGI 6, D-52425 Julich, Germany..
    Ellguth, M.
    Max Planck Inst Mikrostrukturphys, Weinberg 2, D-06120 Halle, Germany.;Johannes Gutenberg Univ Mainz, Inst Phys, Staudingerweg 7, D-55116 Mainz, Germany..
    Crozier, E. D.
    Simon Fraser Univ, Dept Phys, Burnaby, BC V5A 1S6, Canada..
    Mohseni, K.
    Max Planck Inst Mikrostrukturphys, Weinberg 2, D-06120 Halle, Germany..
    Otrokov, M. M.
    Univ Basque Country, CFM, Dept Fis Mat, MPC, San Sebastian 20080, Basque Country, Spain.;Ctr Mixto CSIC UPV EHU, San Sebastian 20080, Basque Country, Spain.;Tomsk State Univ, Tomsk 634050, Russia.;St Petersburg State Univ, St Petersburg 198505, Russia..
    Zubizarreta, X.
    Max Planck Inst Mikrostrukturphys, Weinberg 2, D-06120 Halle, Germany..
    Vergniory, M. G.
    Max Planck Inst Mikrostrukturphys, Weinberg 2, D-06120 Halle, Germany.;DIPC, San Sebastian 20018, Basque Country, Spain..
    Geilhufe, Matthias
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Max Planck Inst Mikrostrukturphys, Weinberg 2, D-06120 Halle, Germany.;KTH Royal Inst Technol, Stockholm Ctr Quantum Mat, Nordita, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden.;Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Chulkov, E. V.
    Univ Basque Country, CFM, Dept Fis Mat, MPC, San Sebastian 20080, Basque Country, Spain.;Ctr Mixto CSIC UPV EHU, San Sebastian 20080, Basque Country, Spain.;Tomsk State Univ, Tomsk 634050, Russia.;DIPC, San Sebastian 20018, Basque Country, Spain..
    Ernst, A.
    Max Planck Inst Mikrostrukturphys, Weinberg 2, D-06120 Halle, Germany.;Johannes Kepler Univ Linz, Inst Theoret Phys, A-4040 Linz, Austria..
    Meyerheim, H. L.
    Max Planck Inst Mikrostrukturphys, Weinberg 2, D-06120 Halle, Germany..
    Parkin, S. S. P.
    Max Planck Inst Mikrostrukturphys, Weinberg 2, D-06120 Halle, Germany..
    Reply to "Comment on 'Instability of the topological surface state in Bi2Se3 upon deposition of gold'"2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 13, article id 136202Article in journal (Refereed)
    Abstract [en]

    In the Comment on our publication [Phys. Rev. B 95, 180202(R) (2017)], R. A. Gordon claims that our main conclusion is not valid, namely that gold atoms deposited in situ on the (0001) surface of single-crystalline Bi2Se3 reside in substitutional sites, i.e., replacing bismuth atoms within the topmost quintuple layer (QL). Based on x-ray absorption near-edge (XANES) spectra and a re-evaluation of extended x-ray absorption fine structure (EXAFS) data above the Au L-III edge, R. A. Gordon concludes that Au resides in a twofold environment as a result of an interface reaction leading to an Au2S-type local structure, in which gold adopts an Au(I) state and is linearly coordinated by selenium atoms. In this Reply, we will confirm the results published in the original paper and their interpretation that Au atoms reside in the substitutional site.

  • 229.
    Pournaghavi, N.
    et al.
    Linnaeus Univ, Dept Phys & Elect Engn, S-39182 Kalmar, Sweden..
    Pertsova, Anna
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    MacDonald, A. H.
    Univ Texas Austin, Dept Phys, Austin, TX 78712 USA..
    Canali, C. M.
    Linnaeus Univ, Dept Phys & Elect Engn, S-39182 Kalmar, Sweden..
    Nonlocal sidewall response and deviation from exact quantization of the topological magnetoelectric effect in axion-insulator thin films2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 20, article id L201102Article in journal (Refereed)
    Abstract [en]

    Topological insulator (TI) thin films with surface magnetism are expected to exhibit a quantized anomalous Hall effect (QAHE) when the magnetizations on the top and bottom surfaces are parallel, and a quantized topological magnetoelectric effect (QTME) when the magnetizations have opposing orientations (axion-insulator phase) and the films are sufficiently thick. We present a unified picture of both effects that associates deviations from exact quantization of the QTME caused by finite thickness with nonlocality in the sidewall current response function. Using realistic tight-binding model calculations, we show that in Bi2Se3 TI thin films, deviations from quantization in the axion-insulator phase are reduced in size when the exchange coupling of tight-binding model basis states to the local magnetization near the surface is strengthened. Stronger exchange coupling also reduces the effect of potential disorder, which is unimportant for the QAHE but detrimental for the QTME, which requires that the Fermi energy lie inside the gap at all positions.

  • 230. Poyhonen, Kim
    et al.
    Weststrom, Alex
    Pershoguba, Sergey S.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Ojanen, Teemu
    Balatsky, Alexander V.
    Skyrmion-induced bound states in a p-wave superconductor2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 21, article id 214509Article in journal (Refereed)
    Abstract [en]

    In s-wave systems, it has been theoretically shown that a ferromagnetic film hosting a skyrmion can induce a bound state embedded in the opposite-spin continuum. In this work, we consider a case of skyrmion-induced state in a p-wave superconductor. We find that the skyrmion induces a bound state that generally resides within the spectral gap and is isolated from all other states, in contrast to the case of conventional superconductors. To this end, we derive an approximate expression for the T matrix, through which we calculate the spin-polarized local density of states which is observable in scanning tunneling microscopy measurements. We find the unique spectroscopic features of the skyrmion-induced bound state and discuss how our predictions could be employed as experimental probes for p-wave superconducting states.

  • 231.
    Pozo, Oscar
    et al.
    Inst Ciencia Mat Madrid, Madrid 28049, Spain.;CSIC, Madrid 28049, Spain..
    Ferreiros, Yago
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Vozmediano, Maria A. H.
    Inst Ciencia Mat Madrid, Madrid 28049, Spain.;CSIC, Madrid 28049, Spain..
    Anisotropic fixed points in Dirac and Weyl semimetals2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 11, article id 115122Article in journal (Refereed)
    Abstract [en]

    The effective low energy description of interacting Dirac and Weyl semimetals is that of massless quantum electrodynamics with several Lorentz breaking material parameters. We perform a renormalization group analysis of Coulomb interaction in anisotropic Dirac and Weyl semimetals and show that the anisotropy persists in the material systems at the infrared fixed point. In addition, a tilt of the fermion cones breaking inversion symmetry induces a magnetoelectric term in the electrodynamics of the material whose magnitude runs to match that of the electronic tilt at the fixed point.

  • 232.
    Principi, Alessandro
    et al.
    Univ Manchester, Sch Phys & Astron, Oxford Rd, Manchester M13 9PL, Lancs, England..
    Bandurin, Denis
    Univ Manchester, Sch Phys & Astron, Oxford Rd, Manchester M13 9PL, Lancs, England.;State Univ, Moscow Inst Phys & Technol, Dolgoprudnyi 141700, Russia..
    Rostami, Habib
    Nordita SU.
    Polini, Marco
    Univ Manchester, Sch Phys & Astron, Oxford Rd, Manchester M13 9PL, Lancs, England.;Graphene Labs, Ist Italiano Tecnol, Via Morego 30, I-16163 Genoa, Italy..
    Pseudo-Euler equations from nonlinear optics: Plasmon-assisted photodetection beyond hydrodynamics2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 7, article id 075410Article in journal (Refereed)
    Abstract [en]

    A great deal of theoretical and experimental efforts have been devoted in the last decades to the study of long-wavelength photodetection mechanisms in field-effect transistors hosting two-dimensional (2D) electron systems. A particularly interesting subclass of these mechanisms is intrinsic and based on the conversion of the incoming electromagnetic radiation into plasmons, which resonantly enhance the photoresponse, and subsequent rectification via hydrodynamic nonlinearities. In this paper, we show that such a conversion and subsequent rectification occur well beyond the frequency regime in which hydrodynamic theory applies. We consider the nonlinear optical response of generic 2D electron systems and derive pseudo-Euler equations of motion for suitable collective variables. These are solved in one- and two-dimensional geometries for the case of graphene and the results are compared with those of hydrodynamic theory. Significant qualitative differences are found, which are amenable to experimental studies. Our theory expands the knowledge of the fundamental physics behind long-wavelength photodetection.

  • 233.
    Putnam, R.
    et al.
    Univ North Florida, Dept Phys, Jacksonville, FL 32224 USA..
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Department of Physics, University of Connecticut, Storrs, Connecticut 06269, USA.
    Haraldsen, J. T.
    Univ North Florida, Dept Phys, Jacksonville, FL 32224 USA..
    Spin channel induced directional dependent spin exchange interactions between divacantly substituted Fe atoms in graphene2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 12, article id 125435Article in journal (Refereed)
    Abstract [en]

    In this study, we show the divacant substitution of Fe impurities atom produces the formation of an electron spin channel along the armchair direction of graphene. This spin channel creates a directional dependent spin exchange between impurities. Using density functional theory, we simulated the electronic and magnetic properties for a supercell of graphene with spatial variation of the Fe atoms along either the armchair or zigzag directions. Overall, we find that the exchange interaction between the two Fe atoms fluctuates from ferromagnetic to antiferromagnetic as a function of the spatial distance in the armchair direction. Given the induced magnetic moment and increased density of states at the Fermi level by the surrounding carbon atoms, we conclude that an RKKY-like interaction may characterize the exchange interactions between the Fe atoms. Furthermore, we examined the same interactions for Fe atoms along the zigzag direction in graphene and found no evidence for an RKKY interaction as this system shows a standard exchange between the transition-metal impurities. Therefore, we determine that the spin channel produced through Fe-substitution in graphene induces a directional-dependent spin interaction, which may provide stability to spintronic and multifunctional devices and applications for graphene.

  • 234. Razzoli, E.
    et al.
    Matt, C. E.
    Sassa, Y.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF. Ecole Polytech Fed Lausanne, Switzerland.
    Tjernberg, Oscar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.
    Drachuck, G.
    Monomo, M.
    Oda, M.
    Kurosawa, T.
    Huang, Y.
    Plumb, N. C.
    Radovic, M.
    Keren, A.
    Patthey, L.
    Mesot, J.
    Shi, M.
    Rotation symmetry breaking in La2-xSrxCuO4 revealed by angle-resolved photoemission spectroscopy2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 22, article id 224504Article in journal (Refereed)
    Abstract [en]

    Using angle-resolved photoemission spectroscopy it is revealed that in the vicinity of optimal doping the electronic structure of La2-x SrxCuO4 cuprate undergoes an electronic reconstruction associated with a wave vector q(a) = (pi, 0). The reconstructed Fermi surface and folded band are distinct to the shadow bands observed in BSCCO cuprates and in underdoped La2-xSrxCuO4 with x <= 0.12, which shift the primary band along the zone diagonal direction. Furthermore, the folded bands appear only with q(a) = (pi, 0) vector, but not with q(b) = (0, pi). We demonstrate that the absence of q(b) reconstruction is not due to thematrix-element effects in the photoemission process, which indicates the fourfold symmetry is broken in the system.

  • 235.
    Reid, Thomas K.
    et al.
    Univ Connecticut, Dept Mat Sci & Engn, Storrs, CT 06269 USA.;Univ Connecticut, Inst Mat Sci, Storrs, CT 06269 USA..
    Alpay, S. Pamir
    Univ Connecticut, Dept Mat Sci & Engn, Storrs, CT 06269 USA.;Univ Connecticut, Inst Mat Sci, Storrs, CT 06269 USA.;Univ Connecticut, Dept Phys, Storrs, CT 06269 USA..
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Nayak, Sanjeev K.
    Univ Connecticut, Dept Mat Sci & Engn, Storrs, CT 06269 USA.;Univ Connecticut, Inst Mat Sci, Storrs, CT 06269 USA..
    First-principles modeling of binary layered topological insulators: Structural optimization and exchange-correlation functionals2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 8, article id 085140Article in journal (Refereed)
    Abstract [en]

    Topological insulators (TIs) are materials that are insulating in the bulk but have zero band-gap surface states with linear dispersion and are protected by time-reversal symmetry. These unique characteristics could pave the way for many promising applications that include spintronic devices and quantum computations. It is important to understand and theoretically describe TIs as accurately as possible to predict properties. Quantum mechanical approaches, specifically first-principles density-functional-theory (DFT)-based methods, have been used extensively to model electronic properties of TIs. Here we provide a comprehensive assessment of a variety of DFT formalisms and how these capture the electronic structure of TIs. We concentrate on Bi2Se3 and Bi2Te3 as examples of prototypical TI materials. We find that the generalized gradient approximation (GGA) and kinetic density functional (metaGGA) increase the thickness of the TI slab, whereas we see the opposite behavior in DFT computations using LDA. Accounting for van der Waals (vdW) interactions overcomes the apparent over-relaxations and retraces the atomic positions toward the bulk. Based on a systematic computational study, we show that GGA with vdW treatment is an appropriate method for structural optimization. However, the vdW corrections recover the experimental bulk parameters, and do not influence the charge density implicitly. Thus, electronic structures derived from the base GGA functional, employing experimental lattice parameters, is sufficient.

  • 236.
    Reid, Thomas K.
    et al.
    Department of Materials Science and Engineering and Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269, USA.
    Alpay, S. Pamir
    Department of Materials Science and Engineering and Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269, USA; Department of Physics, University of Connecticut, Storrs, Connecticut 06269, USA.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Department of Physics, University of Connecticut, Storrs, Connecticut 06269, USA.
    Nayak, Sanjeev K.
    Department of Materials Science and Engineering and Institute of Materials Science, University of Connecticut, Storrs, Connecticut 06269, USA; Department of Physics, University of Connecticut, Storrs, Connecticut 06269, USA.
    Inducing quantum phase transitions in nontopological insulators via atomic control of substructural elements2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, no 23, article id 235402Article in journal (Refereed)
    Abstract [en]

    Topological insulators are an important family of quantum materials that exhibit a Dirac point (DP) in the surface band structure but have a finite band gap in bulk. A large degree of spin-orbit interaction and low band gap is a prerequisite for stabilizing DPs on selective atomically flat cleavage planes. Tuning of the DP in these materials has been suggested via modifications to the atomic structure of the entire system. Using the example of As2Te3 and ZnTe5, which are not TIs, we show that a quantum phase transition can be induced in atomically flat and stepped surfaces, for As2Te3 and ZrTe5, respectively. This is achieved by establishing a framework for controlling electronic properties that is focused on local perturbations at key locations that we call substructural elements. We exemplify this framework through a unique method of isovalent sublayer anion doping and biaxial strain.

  • 237.
    Revelli, A.
    et al.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Loo, C. C.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Kiese, D.
    Univ Cologne, Inst Theoret Phys, D-50937 Cologne, Germany..
    Becker, P.
    Univ Cologne, Inst Geol & Mineral, Sect Crystallog, D-50674 Cologne, Germany..
    Froehlich, T.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Lorenz, T.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Sala, M. Moretti
    Politecn Milan, Dipartimento Fis, I-120133 Milan, Italy..
    Monaco, G.
    Univ Trento, Dipartimento Fis, I-38123 Povo, TN, Italy..
    Buessen, F. L.
    Univ Cologne, Inst Theoret Phys, D-50937 Cologne, Germany..
    Attig, J.
    Univ Cologne, Inst Theoret Phys, D-50937 Cologne, Germany..
    Hermanns, Maria
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Albanova Univ Ctr, Dept Phys, SE-10691 Stockholm, Sweden.;Stockholm Univ, SE-10691 Stockholm, Sweden..
    Streltsov, S. , V
    Khomskii, D. , I
    van den Brink, I. J.
    IFW Dresden, Inst Theoret Solid State Phys, D-01069 Dresden, Germany..
    Braden, M.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    van Loosdrecht, P. H. M.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Trebst, S.
    Univ Cologne, Inst Theoret Phys, D-50937 Cologne, Germany..
    Paramekanti, A.
    Univ Toronto, Dept Phys, Toronto, ON M5S 1A7, Canada..
    Grueninger, M.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Spin-orbit entangled j=1/2 moments in Ba(2)CWeIrO(6): A frustrated fcc quantum magnet2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 8, article id 085139Article in journal (Refereed)
    Abstract [en]

    We establish the double perovskite Ba2CeIrO6 as a nearly ideal model system for j = 1/2 moments, with resonant inelastic x-ray scattering indicating that the ideal j = 1/2 state contributes by more than 99% to the ground-state wave function. The local j = 1/2 moments form an fcc lattice and are found to order antiferromagnetically at T-N = 14 K, more than an order of magnitude below the Curie-Weiss temperature. Model calculations show that the geometric frustration of the fcc Heisenberg antiferromagnet is further enhanced by a next-nearest neighbor exchange, and a significant size of the latter is indicated by ab initio theory. Our theoretical analysis shows that magnetic order is driven by a bond-directional Kitaev exchange and by local distortions via a strong magnetoelastic effect. Both, the suppression of frustration by Kitaev exchange and the strong magnetoelastic effect are typically not expected for j = 1/2 compounds making Ba2CeIrO6 a riveting example for the rich physics of spin-orbit entangled Mott insulators.

  • 238.
    Revelli, A.
    et al.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Sala, M. Moretti
    European Synchrotron Radiat Facil, BP 220, F-38043 Grenoble, France.;Politecn Milan, Dipartimento Fis, I-20133 Milan, Italy..
    Monaco, G.
    Univ Padua, Dipartimento Fis & Astron Galileo Galilei, I-35121 Padua, Italy..
    Magnaterra, M.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Attig, J.
    Univ Cologne, Inst Theoret Phys, D-50937 Cologne, Germany..
    Peterlini, L.
    Univ Cologne, Inst Theoret Phys, D-50937 Cologne, Germany..
    Dey, T.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany.;Indian Sch Mines, Dept Petr Engn, IIT, Dhanbad 826004, Jharkhand, India.;Univ Augsburg, Ctr Elect Correlat & Magnetism, Expt Phys 6, D-86159 Augsburg, Germany..
    Tsirlin, A. A.
    Univ Augsburg, Ctr Elect Correlat & Magnetism, Expt Phys 6, D-86159 Augsburg, Germany..
    Gegenwart, P.
    Univ Augsburg, Ctr Elect Correlat & Magnetism, Expt Phys 6, D-86159 Augsburg, Germany..
    Froehlich, T.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Braden, M.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Grams, C.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Hemberger, J.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Becker, P.
    Univ Cologne, Inst Geol & Mineral, Crystallog Sect, D-50674 Cologne, Germany..
    van Loosdrecht, P. H. M.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Khomskii, D. I.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    van den Brink, J.
    IFW Dresden, Inst Theoret Solid State Phys, D-01069 Dresden, Germany.;Tech Univ Dresden, Inst Theoret Phys, D-01069 Dresden, Germany.;Tech Univ Dresden, Wurzburg Dresden Cluster Excellence Ct Qmat, D-01069 Dresden, Germany..
    Hermanns, Maria
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Grueninger, M.
    Univ Cologne, Inst Phys 2, D-50937 Cologne, Germany..
    Quasimolecular electronic structure of the spin-liquid candidate Ba3InIr2O92022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, no 15, article id 155107Article in journal (Refereed)
    Abstract [en]

    The mixed-valent iridate Ba3InIr2O9 has been discussed as a promising candidate for quantum spin-liquid behavior. The compound exhibits Ir4.5+ ions in face-sharing IrO6 octahedra forming Ir2O9 dimers with three t(2g) holes per dimer. Our results establish Ba3InIr2O9 as a cluster Mott insulator. Strong intradimer hopping delocalizes the three t(2g) holes in quasimolecular dimer states while interdimer charge fluctuations are suppressed by Coulomb repulsion. The magnetism of Ba3InIr2O9 emerges from spin-orbit entangled quasimolecular moments with yet unexplored interactions, opening up a new route to unconventional magnetic properties of 5d compounds. Using single-crystal x-ray diffraction we find the monoclinic space group C2/c already at room temperature. Dielectric spectroscopy shows insulating behavior. Resonant inelastic x-ray scattering reveals a rich excitation spectrum below 1.5 eV with a sinusoidal dynamical structure factor that unambiguously demonstrates the quasimolecular character of the electronic states. Below 0.3 eV, we observe a series of excitations. According to exact diagonalization calculations, such low-energy excitations reflect the proximity of Ba3InIr2O9 to a hopping-induced phase transition based on the condensation of a quasimolecular spin-orbit exciton. The dimer ground state roughly hosts two holes in a bonding j = 1/2 orbital and the third hole in a bonding j = 3/2 orbital.

  • 239.
    Rhim, Jun-Won
    et al.
    Max Planck Inst Phys Komplexer Syst, D-01187 Dresden, Germany.;Inst for Basic Sci Korea, Ctr Correlated Elect Syst, Seoul 08826, South Korea.;Seoul Natl Univ, Dept Phys & Astron, Seoul 08826, South Korea..
    Bardarson, Jens H.
    KTH, School of Engineering Sciences (SCI), Physics. Max Planck Inst Phys Komplexer Syst, D-01187 Dresden, Germany..
    Slager, Robert-Jan
    Max Planck Inst Phys Komplexer Syst, D-01187 Dresden, Germany..
    Unified bulk-boundary correspondence for band insulators2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 11, article id 115143Article in journal (Refereed)
    Abstract [en]

    The bulk-boundary correspondence, a topic of intensive research interest over the past decades, is one of the quintessential ideas in the physics of topological quantum matter. Nevertheless, it has not been proven in all generality and has in certain scenarios even been shown to fail, depending on the boundary profiles of the terminated system. Here, we introduce bulk numbers that capture the exact number of in-gap modes, without any such subtleties in one spatial dimension. Similarly, based on these 1D bulk numbers, we define a new 2D winding number, which we call the pole winding number, that specifies the number of robust metallic surface bands in the gap as well as their topological character. The underlying general methodology relies on a simple continuous extrapolation from the bulk to the boundary, while tracking the evolution of Green's function's poles in the vicinity of the bulk band edges. As a main result we find that all the obtained numbers can be applied to the known insulating phases in a unified manner regardless of the specific symmetries. Additionally, from a computational point of view, these numbers can be effectively evaluated without any gauge fixing problems. In particular, we directly apply our bulk-boundary correspondence construction to various systems, including 1D examples without a traditional bulk-boundary correspondence, and predict the existence of boundary modes on various experimentally studied graphene edges, such as open boundaries and grain boundaries. Finally, we sketch the 3D generalization of the pole winding number by in the context of topological insulators.

  • 240.
    Rostami, Habib
    Nordita SU; Univ Bath, Dept Phys, Bath BA2 7AY, England; Stockholm Univ, Hannes Alfvens Vag 12, S-10691 Stockholm, Sweden..
    Light-induced shear phonon splitting and instability in bilayer graphene2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 16, article id 165418Article in journal (Refereed)
    Abstract [en]

    Coherent engineering of landscape potential in crystalline materials is a rapidly evolving research field. Ultrafast optical pulses can manipulate low-frequency shear phonons in van der Waals layered materials through the dynamical dressing of electronic structure and photoexcited carrier density. In this work, we provide a diagrammatic formalism for nonlinear Raman force and implement it to shear phonon dynamics in bilayer graphene. We predict a controllable splitting of double degenerate shear phonon modes due to light-induced phonon mixing and renormalization according to a coherent nonlinear Raman force mechanism. Intriguingly, we obtain a light-induced shear phonon softening that facilitates structural instability at a critical field amplitude for which the shear phonon frequency vanishes. The phonon splitting and instability strongly depend on the laser intensity, frequency, chemical potential, and temperature of photoexcited electrons. This study motivates future experimental investigation of the optical fine tuning and regulation of shear phonons and layer stacking order in layered van der Waals materials.

  • 241.
    Rostami, Habib
    Nordita SU.
    Theory for shear displacement by light-induced Raman force in bilayer graphene2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, no 15, article id 155405Article in journal (Refereed)
    Abstract [en]

    Coherent excitation of shear phonons in van der Waals layered materials is a nondestructive mechanism to fine-tune the lattice structure and the electronic state of the system. We develop a diagrammatic theory for the displacive Raman force and apply it to the shear phonon's dynamics. We obtain a noticeable light-induced Raman force of the order of F similar to 10-100 nN/nm(2) leading to a large rectified shear displacement Q(0) in bilayer graphene. In analogy to the photogalvanic effect, we decompose the Raman force to circular and linear components where the former vanishes due to the lattice symmetry in bilayer graphene. We show that the laser frequency and polarization can effectively tune Q(0) in different electronic doping, temperature, and scattering rates. The finite rectified shear displacement induces a Dirac crossing pair in the low-energy dispersion that photoemission spectroscopy can probe. Our systematic formalism of Raman force can simulate the coherent manipulation of stacking order in the heterostructures of layered materials by laser irradiation.

  • 242.
    Rostami, Habib
    et al.
    Stockholm University, Stockholm, SE-106 91, Sweden;Nordita SU.
    Cappelluti, Emmanuele
    CNR, Ist Struttura Mat, I-34149 Trieste, Italy..
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, SE-10691 Stockholm, Sweden..
    Helical metals and insulators: Sheet singularity of the inflated Berry monopole2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 24, article id 245114Article in journal (Refereed)
    Abstract [en]

    We study phases of interacting Dirac matter that host Berry signatures. We predict a topological Lifshitz phase transition caused by the changes of a Dirac cone intersection from a semimetallic phase to helical insulating or metallic phases. These helical phases provide examples of a gapless topological phase where the spectral gap is not required for a topological protection. To realize nodal helical phases one would need to consider isotropic infinite-range interparticle. interaction. This interaction could emerge because of a momentum conserving scattering of electrons from a bosonic mode. For repulsive/attractive inter-particle interaction in density/pseudospin channel, the system undergoes a transition to the helical insulator phase. For an attractive density-density interaction, a metallic phase forms that hosts a nodal circle and a nodal sphere in two and three dimensions, respectively. A sheet singularity of Berry curvature is highlighted as a peculiar feature of the nodal sphere phase in three dimensions and represents the extension of the Berry monopole singularities into an inflated monopole. To illustrate the properties of these helical phases we investigate Landau levels in both metallic and insulating phases. Our study provides an extension of the paradigm in the interacting Dirac matter and makes an interesting connection to inflated topological singularities in cosmology.

  • 243.
    Rostami, Habib
    et al.
    Nordita SU Stockholm Univ, Hannes Alfvens Vag 12, S-12 Stockholm, Sweden..
    Guinea, Francisco
    Imdea Nanosci, Faraday 9, Madrid 28047, Spain.;Donostia Int Phys Ctr, Paseo Manuel de Lardizabal 4, San Sebastian 20018, Spain.;Ikerbasque, Basque Fdn Sci, Bilbao 48009, Spain..
    Cappelluti, Emmanuele
    CNR, Ist Struttura Mat, ISM CNR, I-34149 Trieste, Italy..
    Strain-driven chiral phonons in two-dimensional hexagonal materials2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 19, article id 195431Article in journal (Refereed)
    Abstract [en]

    Hexagonal two-dimensional materials with broken inversion symmetry (as BN or transition metal dichalcogenides) are known to sustain chiral phonons with finite angular momentum, adding a further useful degree of freedom to the extraordinary entangled (electrical, optical, magnetic, and mechanical) properties of these compounds. However, because of lattice symmetry constraints, such chiral modes are constrained to the corners of the Brillouin zone, allowing little freedom for manipulating the chiral features. In this paper, we show how the application of uniaxial strain leads to the existence of unique chiral modes in the vicinity of the zone center. We also show that such strain-induced chiral modes, unlike the ones pinned at the K points, can be efficiently manipulated by modifying the strain itself, which determines the position of these modes in the Brillouin zone. The present paper results add a technique for the engineering of the quantum properties of two-dimensional lattices.

  • 244.
    Rostami, Habib
    et al.
    Nordita SU.
    Volckaert, Klara
    Aarhus Univ, Dept Phys & Astron, Interdisciplinary Nanosci Ctr, DK-8000 Aarhus C, Denmark..
    Lanata, Nicola
    Aarhus Univ, Dept Phys & Astron, Interdisciplinary Nanosci Ctr, DK-8000 Aarhus C, Denmark..
    Mahatha, Sanjoy K.
    Aarhus Univ, Dept Phys & Astron, Interdisciplinary Nanosci Ctr, DK-8000 Aarhus C, Denmark..
    Sanders, Charlotte E.
    STFC Rutherford Appleton Lab, Cent Laser Facil, Harwell 0X11 0QX, Berks, England..
    Bianchi, Marco
    Aarhus Univ, Dept Phys & Astron, Interdisciplinary Nanosci Ctr, DK-8000 Aarhus C, Denmark..
    Lizzit, Daniel
    Elettra Sincrotrone Trieste SS, 14 Km 163-5, I-34149 Trieste, Italy..
    Bignardi, Luca
    Elettra Sincrotrone Trieste SS, 14 Km 163-5, I-34149 Trieste, Italy.;Univ Trieste, Dept Phys, Via Valerio 2, I-34127 Trieste, Italy..
    Lizzit, Silvano
    Elettra Sincrotrone Trieste SS, 14 Km 163-5, I-34149 Trieste, Italy..
    Miwa, Jill A.
    STFC Rutherford Appleton Lab, Cent Laser Facil, Harwell 0X11 0QX, Berks, England..
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Hofmann, Philip
    Aarhus Univ, Dept Phys & Astron, Interdisciplinary Nanosci Ctr, DK-8000 Aarhus C, Denmark..
    Ulstrup, Soren
    Aarhus Univ, Dept Phys & Astron, Interdisciplinary Nanosci Ctr, DK-8000 Aarhus C, Denmark..
    Layer and orbital interference effects in photoemission from transition metal dichalcogenides2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 23, article id 235423Article in journal (Refereed)
    Abstract [en]

    In this work, we provide an effective model to evaluate the one-electron dipole matrix elements governing optical excitations and the photoemission process of single-layer (SL) and bilayer (BL) transition metal dichalcogenides. By utilizing a k . p Hamiltonian, we calculate the photoemission intensity as observed in angle-resolved photoemission from the valence bands around the (K) over bar valley of MoS2. In SL MoS2, we find a significant masking of intensity outside the first Brillouin zone, which originates from an in-plane interference effect between photoelectrons emitted from the Mo d orbitals. In BL MoS2, an additional interlayer interference effect leads to a distinctive modulation of intensity with photon energy. Finally, we use the semiconductor Bloch equations to model the optical excitation in a time- and angle-resolved pump-probe photoemission experiment. We find that the momentum dependence of an optically excited population in the conduction band leads to an observable dichroism in both SL and BL MoS2.

  • 245. Roy, B.
    et al.
    Goswami, P.
    Juričić, Vladimir
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Interacting Weyl fermions: Phases, phase transitions, and global phase diagram2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 20, article id 201102Article in journal (Refereed)
    Abstract [en]

    We study the effects of short-range interactions on a generalized three-dimensional Weyl semimetal, where the band touching points act as the (anti)monopoles of Abelian Berry curvature of strength n. We show that any local interaction has a negative scaling dimension -2/n. Consequently, all Weyl semimetals are stable against weak short-range interactions. For sufficiently strong interactions, we demonstrate that the Weyl semimetal either undergoes a first-order transition into a band insulator or a continuous transition into a symmetry breaking phase. A translational symmetry breaking axion insulator and a rotational symmetry breaking semimetal are two prominent candidates for the broken symmetry phase. At the one-loop order, the correlation length exponent for continuous transitions is ν=n/2, indicating their non-Gaussian nature for any n>1. We also discuss the scaling of the thermodynamic and transport quantities in general Weyl semimetals as well as inside broken symmetry phases.

  • 246. Roy, B.
    et al.
    Goswami, P.
    Juričić, Vladimir
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden.
    Itinerant quantum multicriticality of two-dimensional Dirac fermions2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 20, article id 205117Article in journal (Refereed)
    Abstract [en]

    We analyze emergent quantum multicriticality for strongly interacting, massless Dirac fermions in two spatial dimensions (d=2) within the framework of Gross-Neveu-Yukawa models, by considering the competing order parameters that give rise to fully gapped (insulating or superconducting) ground states. We focus only on those competing orders which can be rotated into each other by generators of an exact or emergent chiral symmetry of massless Dirac fermions, and break O(S1) and O(S2) symmetries in the ordered phase. Performing a renormalization-group analysis by using the ϵ=(3-d) expansion scheme, we show that all the coupling constants in the critical hyperplane flow toward a new attractive fixed point, supporting an enlarged O(S1+S2) chiral symmetry. Such a fixed point acts as an exotic quantum multicritical point (MCP), governing the continuous semimetal-insulator as well as insulator-insulator (for example, antiferromagnet to valence bond solid) quantum phase transitions. In comparison with the lower symmetric semimetal-insulator quantum critical points, possessing either O(S1) or O(S2) chiral symmetry, the MCP displays enhanced correlation length exponents, and anomalous scaling dimensions for both fermionic and bosonic fields. We discuss the scaling properties of the ratio of bosonic and fermionic masses, and the increased dc resistivity at the MCP. By computing the scaling dimensions of different local fermion bilinears in the particle-hole channel, we establish that most of the four fermion operators or generalized density-density correlation functions display faster power-law decays at the MCP compared to the free fermion and lower symmetric itinerant quantum critical points. Possible generalization of this scenario to higher-dimensional Dirac fermions is also outlined.

  • 247. Roy, B.
    et al.
    Juričić, Vladimir
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Roslagstullsbacken 23, Stockholm, 10691, Sweden.
    Fermionic multicriticality near Kekulé valence-bond ordering on a honeycomb lattice2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 24, article id 241103Article in journal (Refereed)
    Abstract [en]

    We analyze the possibility of emergent quantum multicritical points (MCPs) with enlarged chiral symmetry, when strongly interacting gapless Dirac fermions acquire a comparable propensity toward the nucleation of Kekulé valence-bond solid (KVBS) and charge-density-wave (Nb=1) or s-wave pairing (Nb=2) or antiferromagnet (Nb=3) in a honeycomb lattice, where Nb counts the number of bosonic order-parameter components. Besides the cubic terms present in the order-parameter description of KVBS due to the breaking of a discrete Z3 symmetry, quantum fluctuations generate new cubic vertices near the high-symmetry MCPs. All cubic terms are strongly relevant at the bare level near three spatial dimensions, about which we perform a leading-order renormalization group analysis of coupled Gross-Neveu-Yukawa field theory. We show that due to nontrivial Yukawa interactions among gapless bosonic and fermionic degrees of freedom, all cubic terms ultimately become irrelevant at an O(2+Nb) symmetric MCP, at leas near two spatial dimensions, where Nb=1,2,3. Therefore, MCPs with an enlarged O(2+Nb) symmetry near KVBS ordering are stable.

  • 248.
    Roy, Bitan
    et al.
    Lehigh Univ, Dept Phys, Bldg 16, Bethlehem, PA 18015 USA..
    Juricic, Vladimir
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Univ Tecn Federico Santa Maria, Dept Fis, Casilla 110, Valparaiso, Chile..
    Mixed-parity octupolar pairing and corner Majorana modes in three dimensions2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 18, article id L180503Article in journal (Refereed)
    Abstract [en]

    We identify time-reversal symmetry breaking mixed-parity superconducting states that feature eight Majorana corner modes in properly cleaved three-dimensional cubic crystals. Namely, when an odd-parity isotropic p-wave pairing coexists with cubic symmetry preserving even-parity octupolar d(x2-y2) + id(3z2-r2) pairing, the gapless surface Majorana modes of the former get localized at the eight corners, thus yielding an intrinsic third-order topological superconductor (TOTSC). A cousin d(xy) + id(3z2-r2) pairing also accommodating eight corner Majorana modes, by virtue of breaking the cubic symmetry, in contrast, yields an extrinsic TOTSC. We identify a doped octupolar (topological or trivial) Dirac insulator as a suitable platform to sustain such unconventional superconductors, realized from an intraunit cell pairing. Finally, we argue that the proposed TOTSC can be experimentally realizable in NaCl and other structurally similar compounds under high pressure.

  • 249. Roy, Bitan
    et al.
    Juricic, Vladimir
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Optical conductivity of an interacting Weyl liquid in the collisionless regime2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 15, article id 155117Article in journal (Refereed)
    Abstract [en]

    Optical conductivity (OC) can serve as a measure of correlation effects in a wide range of condensed-matter systems. We show that the long-range tail of the Coulomb interaction yields a universal correction to the OC in a three-dimensional Weyl semimetal sigma(Omega) = sigma(0)(Omega)[1 + 1/N+1], where sigma(0)(Omega) = Ne-0(2)Omega/(12hv) is the OC in the noninteracting system, with v as the actual (renormalized) Fermi velocity of Weyl quasiparticles at frequency Omega, and e(0) is the electron charge in vacuum. Such universal enhancement of OC, which depends only on the number of Weyl nodes near the Fermi level (N), is a remarkable consequence of an intriguing conspiracy among the quantum-critical nature of an interacting Weyl liquid, marginal irrelevance of the long-range Coulomb interaction, and violation of hyperscaling in three dimensions, and can directly be measured in recently discovered Weyl as well as Dirac materials. By contrast, a local density-density interaction produces a nonuniversal correction to the OC, stemming from the nonrenormalizable nature of the corresponding interacting field theory.

  • 250.
    Roy, Bitan
    et al.
    Max Planck Inst Phys Komplexer Syst, Nothnitzer Str 38, D-01187 Dresden, Germany. .
    Juricic, Vladimir
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden.
    Unconventional superconductivity in nearly flat bands in twisted bilayer aphene2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 12, article id 121407Article in journal (Refereed)
    Abstract [en]

    Flat electronic bands can accommodate a plethora of interaction-driven quantum phases, since kinetic energy is quenched therein and electronic interactions therefore prevail. Twisted bilayer graphene, near the so-called "magic angles", features slow Dirac fermions close to the charge-neutrality point that persist up to high energies. Starting from a continuum model of slow but strongly interacting Dirac fermions, we show that with increasing chemical doping away from the charge-neutrality point, a time-reversal symmetry breaking, valley pseudospin-triplet, topological p + ip superconductor gradually sets in, when the system resides at the brink of an antiferromagnetic ordering (due to Hubbard repulsion), in qualitative agreement with recent experimental findings. The p ip paired state exhibits quantized spin and thermal Hall conductivities, and polar Kerr and Faraday rotations. Our conclusions should also be applicable for other correlated two-dimensional Dirac materials.

2345678 201 - 250 of 353
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