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  • 51.
    Cardias, Ramon
    et al.
    KTH. Univ Paris Saclay, CEA, CNRS, SPEC, F-91191 Gif Sur Yvette, France..
    Szilva, Attila
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Bergman, Anders
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Kvashnin, Yaroslav
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Fransson, Jonas
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Streib, Simon
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Delin, Anna
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. KTH, Centres, SeRC - Swedish e-Science Research Centre.
    Katsnelson, Mikhail I.
    Radboud Univ Nijmegen, Inst Mol & Mat, Heyendaalseweg 135, NL-6525 AJ Nijmegen, Netherlands..
    Thonig, Danny
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Örebro Univ, Sch Sci & Technol, Fakultetsgatan 1, SE-70281 Örebro, Sweden..
    Klautau, Angela Burlamaqui
    Univ Fed Para, Fac Fis, BR-66075110 Belem, PA, Brazil..
    Eriksson, Olle
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden.;Örebro Univ, Sch Sci & Technol, Fakultetsgatan 1, SE-70281 Örebro, Sweden..
    Nordstrom, Lars
    Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
    Comment on "Proper and improper chiral magnetic interactions"2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 2, article id 026401Article in journal (Refereed)
    Abstract [en]

    In a recent paper by dos Santos Dias et al. [Phys. Rev. B 103, L140408 (2021)], a critique of earlier works analyzing low-energy spin Hamiltonians is put forth. To be precise, it is the large noncollinear contributions to the Dzyaloshinskii-Moriya interaction (DMI) that is the main concern of dos Santos Dias et al. In this Comment, we clarify the microscopic mechanisms for the large DMI that can be found in noncollinear magnets. Furthermore, we outline the complementary nature of the different parametrizations of a spin Hamiltonian, with strengths and weaknesses of both approaches. Specifically, we stress the physical insight in the interpretation of the DMI, when decomposed in microscopic electron and spin densities and currents.

  • 52. Castin, N.
    et al.
    Messina, L.
    Domain, C.
    Pasianot, R. C.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Improved atomistic Monte Carlo models based on ab-initio -trained neural networks: Application to FeCu and FeCr alloys2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 21, article id 214117Article in journal (Refereed)
    Abstract [en]

    We significantly improve the physical models underlying atomistic Monte Carlo (MC) simulations, through the use of ab initio fitted high-dimensional neural network potentials (NNPs). In this way, we can incorporate energetics derived from density functional theory (DFT) in MC, and avoid using empirical potentials that are very challenging to design for complex alloys. We take significant steps forward from a recent work where artificial neural networks (ANNs), exclusively trained on DFT vacancy migration energies, were used to perform kinetic MC simulations of Cu precipitation in Fe. Here, a more extensive transfer of knowledge from DFT to our cohesive model is achieved via the fitting of NNPs, aimed at accurately mimicking the most important aspects of the ab initio predictions. Rigid-lattice potentials are designed to monitor the evolution during the simulation of the system energy, thus taking care of the thermodynamic aspects of the model. In addition, other ANNs are designed to evaluate the activation energies associated with the MC events (migration towards first-nearest-neighbor positions of single point defects), thereby providing an accurate kinetic modeling. Because our methodology inherently requires the calculation of a substantial amount of reference data, we design as well lattice-free potentials, aimed at replacing the very costly DFT method with an approximate, yet accurate and considerably more computationally efficient, potential. The binary FeCu and FeCr alloys are taken as sample applications considering the extensive literature covering these systems.

  • 53.
    Chen, Siyu
    et al.
    Univ Cambridge, Cavendish Lab, TCM Grp, JJ Thomson Ave, Cambridge CB3 0HE, England..
    Bouhon, Adrien
    Stockholm Univ, Nordic Inst Theoret Phys Nordita, Hannes Alfvens Vag 12, SE-10691 Stockholm, Sweden.;KTH Royal Inst Technol, 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..
    Non-Abelian braiding of Weyl nodes via symmetry-constrained phase transitions2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 8, article id L081117Article in journal (Refereed)
    Abstract [en]

    Weyl semimetals are arguably the most paradigmatic form of a gapless topological phase. While the stability of Weyl nodes, as quantified by their topological charge, has been extensively investigated, recent interest has shifted to the manipulation of the location of these Weyl nodes for non-Abelian braiding. To accomplish this braiding it is necessary to drive significant Weyl node motion using realistic experimental parameter changes. We show that a family of phase transitions characterized by certain symmetry constraints impose that the Weyl nodes have to reorganize by a large amount, shifting from one high-symmetry plane to another. Additionally, for a subset of pairs of nodes with nontrivial Euler class topology, this reorganization can only occur through a braiding process with adjacent nodes. As a result, the Weyl nodes are forced to move a large distance across the Brillouin zone and to braid, all driven by small temperature changes, a process we illustrate with Cd2Re2O7.

  • 54.
    Claisse, Antoine
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Schuler, Thomas
    Lopes, Denise Adorno
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Transport properties in dilute UN(X) solid solutions (X = Xe, Kr)2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 17, article id 174302Article in journal (Refereed)
    Abstract [en]

    Uranium nitride (UN) is a candidate fuel for current GEN III fission reactors, for which it is investigated as an accident-tolerant fuel, as well as for future GEN IV reactors. In this study, we investigate the kinetic properties of gas fission products (Xe and Kr) in UN. Binding and migration energies are obtained using density functional theory, with an added Hubbard correlation to model f electrons, and the occupation matrix control scheme to avoid metastable states. These energies are then used as input for the self-consistent mean field method which enables to determine transport coefficients for vacancy-mediated diffusion of Xe and Kr on the U sublattice. The magnetic ordering of the UN structure is explicitly taken into account, for both energetic and transport properties. Solute diffusivities are compared with experimental measurements and the effect of various parameters on the theoretical model is carefully investigated. We find that kinetic correlations are very strong in this system, and that despite atomic migration anisotropy, macroscopic solute diffusivities show limited anisotropy. Our model indicates that the discrepancy between experimental measurements probably results from different irradiation conditions, and hence different defect concentrations.

  • 55.
    Colmenarez, Luis
    et al.
    Max Planck Inst Phys Komplexer Syst, Nothnitzer Str 38, D-01187 Dresden, Germany..
    Luitz, David J.
    Max Planck Inst Phys Komplexer Syst, Nothnitzer Str 38, D-01187 Dresden, Germany.;Univ Bonn, Phys Inst, Nussallee 12, D-53115 Bonn, Germany..
    Khaymovich, Ivan
    Max Planck Inst Phys Komplexer Syst, Nothnitzer Str 38, D-01187 Dresden, Germany.;Russian Acad Sci, Inst Phys Microstructures, GSP-105, Nizhnii Novgorod 603950, Russia.;Stockholm Univ, Nordita, Hannes Alfvens Vag 12, SE-10691 Stockholm, Sweden..
    De Tomasi, Giuseppe
    Univ Illinois, Dept Phys, Urbana, IL 61801 USA..
    Subdiffusive Thouless time scaling in the Anderson model on random regular graphs2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 17, article id 174207Article in journal (Refereed)
    Abstract [en]

    The scaling of the Thouless time with system size is of fundamental importance to characterize dynamical properties in quantum systems. In this work, we study the scaling of the Thouless time in the Anderson model on random regular graphs with on-site disorder. We determine the Thouless time from two main quantities: the spectral form factor and the power spectrum. Both quantities probe the long-range spectral correlations in the system and allow us to determine the Thouless time as the timescale after which the system is well described by random matrix theory. We find that the scaling of the Thouless time is consistent with the existence of a subdiffusive regime anticipating the localized phase. Furthermore, to reduce finite-size effects, we break energy conservation by introducing a Floquet version of the model and show that it hosts a similar subdiffusive regime.

  • 56. Commeau, Benjamin
    et al.
    Geilhufe, R. Matthias
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Fernando, Gayanath W.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm University, Sweden.
    Structural and electronic properties of alpha-(BEDT-TTF)(2)I-3, ss-(BEDT-TTF)(2)I-3, and kappa-(BEDT-TTF)(2)X-3 (X = I, F, Br, Cl) organic charge transfer salts2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 12, article id 125135Article in journal (Refereed)
    Abstract [en]

    (BEDT-TFF)(2)I-3 charge transfer salts are reported to show superconductivity and pressure-induced quasi-twodimensional Dirac cones at the Fermi level. By performing state of the art ab initio calculations in the framework of density functional theory, we investigate the structural and electronic properties of the three structural phases alpha, beta, and kappa(.) We furthermore report about the irreducible representations of the corresponding electronic band structures, symmetry of their crystal structure, and the origin of band crossings. Additionally, we discuss the chemically induced strain in kappa-(BEDT-TTF)(2)I-3 achieved by replacing the iodine layer with other halogens: fluorine, bromine, and chlorine. In the case of kappa-(BEDT-TTF)(2)F-3, we identify topologically protected crossings within the band structure. These crossings are forced to occur due to the nonsymmorphic nature of the crystal. The calculated electronic structures presented here are added to the organic materials database (OMDB).

  • 57. Csire, Gabor
    et al.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Ujfalussy, Balazs
    First-principles approach to thin superconducting slabs and heterostructures2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 14, article id 140502Article in journal (Refereed)
    Abstract [en]

    We present a fully first-principles method for superconducting thin films. The layer dependent phonon spectrum is calculated to determine the layer dependence of the electron-phonon coupling for such systems, which is coupled to the Kohn-Sham-Bogoliubov-de Gennes equations, and it is solved in a parameter-free way. The theory is then applied to different surface facets of niobium slabs and to niobium-gold heterostructures. We investigate the dependence of the transition temperature on the thickness of the slabs and the inverse proximity effect observed in thin superconducting heterostructures.

  • 58.
    Curcio, Davide
    et al.
    Aarhus Univ, Interdisciplinary Nanosci Ctr, Dept Phys & Astron, Ny Munkegade 120, DK-8000 Aarhus C, Denmark..
    Lanata, Nicola
    Aarhus Univ, Dept Phys & Astron, DK-8000 Aarhus C, Denmark.;Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden.;Nordita SU.
    Hofmann, Philip
    Aarhus Univ, Interdisciplinary Nanosci Ctr, Dept Phys & Astron, Ny Munkegade 120, DK-8000 Aarhus C, Denmark..
    Ultrafast electronic linewidth broadening in the C 1s core level of graphene2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 16, article id L161104Article in journal (Refereed)
    Abstract [en]

    We show that the presence of a transiently excited hot electron gas in graphene leads to a substantial broadening of the C 1s line probed by time-resolved x-ray photoemission spectroscopy. The broadening is found to be caused by an exchange of energy and momentum between the photoemitted core electron and the hot electron gas, rather than by vibrational excitations. This interpretation is supported by a quantitative line-shape analysis that accounts for the presence of the excited electrons. Fitting the spectra to this model directly yields the electronic temperature of the system, in good agreement with electronic temperature values obtained from valence band data. Furthermore, we show how the momentum change of the outgoing core electrons leads to a detectable but very small change in the time-resolved photoelectron diffraction pattern and to a nearly complete elimination of the core level binding energy variation associated with the presence of a narrow sigma band in the C is state.

  • 59.
    Dai, Jin
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Ding, Fei
    Bozhevolnyi, Sergey I.
    Yan, Min
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Ultrabroadband super-Planckian radiative heat transfer with artificial continuum cavity states in patterned hyperbolic metamaterials2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 24, article id 245405Article in journal (Refereed)
    Abstract [en]

    Localized cavity resonances due to nanostructures at material surfaces can greatly enhance radiative heat transfer (RHT) between two closely placed bodies owing to stretching of cavity states in momentum space beyond the light line. Based on such understanding, we numerically demonstrate the possibility of ultrabroadband super-Planckian RHT between two plates patterned with trapezoidal-shaped hyperbolic metamaterial (HMM) arrays. The phenomenon is rooted not only in HMM's high effective index for creating subwavelength resonators but also its extremely anisotropic isofrequency contour. The two properties enable one to create photonic bands with a high spectral density to populate a desired thermal radiation window. At submicron gap sizes between such two plates, the artificial continuum states extend outside the light cone, tremendously increasing overall RHT. Our study reveals that structured HMM offers unprecedented potential in achieving a controllable super-Planckian radiative heat transfer for thermal management at nanoscale.

  • 60.
    Dai, Jin
    et al.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Dyakov, Sergey A.
    Bozhevolnyi, Sergey I.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Near-field radiative heat transfer between metasurfaces: A full-wave study based on two-dimensional grooved metal plates2016In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 94, no 12, article id 125431Article in journal (Refereed)
    Abstract [en]

    Metamaterials possess artificial bulk and surface electromagnetic states. Tamed dispersion properties of surface waves allow one to achieve a controllable super-Planckian radiative heat transfer (RHT) process between two closely spaced objects. We numerically demonstrate enhanced RHT between two two-dimensional grooved metal plates by a full-wave scattering approach. The enhancement originates from both transverse-magnetic spoof surface-plasmon polaritons and a series of transverse-electric bonding-and anti-bonding-waveguide modes at surfaces. The RHT spectrum is frequency selective and highly geometrically tailorable. Our simulation also reveals thermally excited nonresonant surface waves in constituent metallic materials may play a prevailing role for RHT at an extremely small separation between two metal plates, rendering metamaterial modes insignificant for the energy-transfer process.

  • 61.
    D'Ambrosio, Federico
    et al.
    Univ Utrecht, Dept Informat & Comp Sci, Princetonpl 5, NL-3584 CC Utrecht, Netherlands..
    Juricic, Vladimir
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden..
    Barkema, Gerard T.
    Univ Utrecht, Dept Informat & Comp Sci, Princetonpl 5, NL-3584 CC Utrecht, Netherlands..
    Discontinuous evolution of the structure of stretching polycrystalline graphene2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 16, article id 161402Article in journal (Refereed)
    Abstract [en]

    Polycrystalline graphene has an inherent tendency to buckle, i.e., develop out-of-plane, three-dimensional structure. A force applied to stretch a piece of polycrystalline graphene influences the out-of-plane structure. Even if the graphene is well relaxed, this happens in nonlinear fashion: Occasionally, a tiny increase in stretching force induces a significant displacement, in close analogy to avalanches, which in turn can create vibrations in the surrounding medium. We establish this effect in computer simulations: By continuously changing the strain, we follow the displacements of the carbon atoms that turn out to exhibit a discontinuous evolution. Furthermore, the displacements exhibit a hysteretic behavior upon the change from low to high stress and back. These behaviors open up another direction in studying dynamical elasticity of polycrystalline quasi-two-dimensional systems, and in particular the implications on their mechanical and thermal properties.

  • 62.
    Das, Adway Kumar
    et al.
    Indian Inst Sci Educ & Res Kolkata, Mohanpur 741246, India..
    Ghosh, Anandamohan
    Indian Inst Sci Educ & Res Kolkata, Mohanpur 741246, India..
    Khaymovich, Ivan M.
    Su, Nordita.
    Robust nonergodicity of the ground states in the β ensemble2024In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 109, no 6, article id 064206Article in journal (Refereed)
    Abstract [en]

    In various chaotic quantum many-body systems, the ground states show nontrivial athermal behavior despite the bulk states exhibiting thermalization. Such athermal states play a crucial role in quantum information theory and its applications. Moreover, any generic quantum many-body system in the Krylov basis is represented by a tridiagonal Lanczos Hamiltonian, which is analogous to the matrices from the ensemble, a well-studied random-matrix model with level repulsion tunable via the parameter . Motivated by this, here we focus on the localization properties of the ground and anti-ground states of the ensemble. Both analytically and numerically we show that both the edge states demonstrate nonergodic (fractal) properties for similar to O(1), while the typical bulk states are ergodic. Surprisingly, the fractal dimension of the edge states remains three times smaller than that of the bulk states irrespective of the global phase of the ensemble. In addition to the fractal dimensions, we also consider the distribution of the localization centers of the spectral edge states, their mutual separation, as well as the spatial and correlation properties of the first excited states.

  • 63.
    Das, Aritra
    et al.
    Indian Inst Sci, Bengaluru 560012, India.;Univ Maryland, Dept Phys, College Pk, MD 20742 USA..
    Borla, Umberto
    Tech Univ Munich, Phys Dept, D-85748 Garching, Germany.;Munich Ctr Quantum Sci & Technol MCQST, D-80799 Munich, Germany..
    Moroz, Sergej
    Nordita SU.
    Fractionalized holes in one-dimensional Z2 gauge theory coupled to fermion matter: Deconfined dynamics and emergent integrability2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 6, article id 064302Article in journal (Refereed)
    Abstract [en]

    We investigate the interplay of quantum one-dimensional discrete Z2 gauge fields and fermion matter near full filling in terms of deconfined fractionalized hole excitations that constitute mobile domain walls between vacua that break spontaneously translation symmetry. In the limit of strong string tension, we uncover emergent integrable correlated hopping dynamics of holes which is complementary to the constrained XXZ description in terms of bosonic dimers. We analyze numerically quantum dynamics of spreading of an isolated hole together with the associated time evolution of entanglement and provide analytical understanding of its salient features. We also study the model enriched with a short-range interaction and clarify the nature of the resulting ground state at low filling of holes and identify deconfined hole excitations near the hole filling nu h = 1/3.

  • 64.
    De Luca, Eleonora
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Sanatinia, Reza
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Mensi, Mounir
    KTH, School of Engineering Sciences (SCI), Applied Physics, Laser Physics.
    Anand, Srinivasan
    KTH, School of Engineering Sciences (SCI), Applied Physics, Photonics.
    Swillo, Marcin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Modal phase matching in nanostructured zinc-blende semiconductors for second-order nonlinear optical interactions2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 7, article id 075303Article in journal (Refereed)
    Abstract [en]

    We demonstrate enhanced second-harmonic generation in arrays of nanowaveguides satisfying modal-phase-matching condition, both theoretically and experimentally. The overlap of interacting fields defined by the fundamental mode of the pump and the second-order mode of the second-harmonic wave is enhanced by the longitudinal component of the nonlinear polarization density. For guided modes with significant longitudinal electric field components, the overlap of fields is comparable to that obtained in the quasi-phase-matching technique leading to higher conversion efficiencies. Thus, the presented method is preferable to achieve higher conversion efficiency in second-order nonlinear processes in nanowaveguides.

  • 65.
    De Tomasi, Giuseppe
    et al.
    Univ Illinois, Dept Phys, Urbana, IL 61801 USA..
    Khaymovich, Ivan M.
    SU Nordita; Max Planck Inst Phys Komplexer Syst, Nothnitzer Str 38, D-01187 Dresden, Germany.;Russian Acad Sci, Inst Phys Microstruct, GSP-105, Nizhnii Novgorod 603950, Russia.;Stockholm Univ, Nordita, Hannes Alfvens Vag 12, S-10691 Stockholm, Sweden..
    Non-Hermitian Rosenzweig-Porter random-matrix ensemble: Obstruction to the fractal phase2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, no 9, article id 094204Article in journal (Refereed)
    Abstract [en]

    We study the stability of nonergodic but extended (NEE) phases in non-Hermitian systems. For this purpose, we generalize the so-called Rosenzweig-Porter random-matrix ensemble, known to carry a NEE phase along with the Anderson localized and ergodic ones, to the non-Hermitian case. We analyze, both analytically and numerically, the spectral and multifractal properties of the non-Hermitian case. We show that the ergodic and localized phases are stable against the non-Hermitian nature of matrix entries. However, the stability of the fractal phase depends on the choice of the diagonal elements. For purely real or imaginary diagonal potential, the fractal phase is intact, while for a generic complex diagonal potential the fractal phase disappears, giving way to a localized one.

  • 66.
    De Tomasi, Giuseppe
    et al.
    Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801-3080, USA.
    Khaymovich, Ivan M.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Nordita SU; Stockholm University, Hannes Alfvéns väg 12, SE-106 91 Stockholm, Sweden; Institute for Physics of Microstructures, Russian Academy of Sciences, 603950 Nizhny Novgorod, GSP-105, Russia.
    Non-Hermiticity induces localization: Good and bad resonances in power-law random banded matrices2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, no 18, article id L180202Article in journal (Refereed)
    Abstract [en]

    The power-law random banded matrix (PLRBM) is a paradigmatic ensemble to study the Anderson localization transition (AT). In d dimensions, the PLRBMs are random matrices with algebraic decaying off-diagonal elements Hnm∼1/|n-m|α, having AT at α=d. In this work, we investigate the fate of the PLRBM to non-Hermiticity (nH). We consider the case where the random on-site diagonal potential takes complex values, mimicking an open system, subject to random gain-loss terms. We understand the model analytically by generalizing the Anderson-Levitov resonance counting technique to the nH case. We identify two competing mechanisms due to nH: favoring localization and delocalization. The competition between the two gives rise to AT at d/2≤α≤d. The value of the critical α depends on the strength of the on-site potential, like in Hermitian disordered short-range models in d>2. Within the localized phase, the wave functions are algebraically localized with an exponent α even for α<d. This result provides an example of non-Hermiticity-induced localization and finds immediate application in phase transitions driven by weak measurements.

  • 67.
    De Tomasi, Giuseppe
    et al.
    Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801-3080, USA.
    Khaymovich, Ivan M.
    Nordita, SU.
    Stable many-body localization under random continuous measurements in the no-click limit2024In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 109, no 17, article id 174205Article in journal (Refereed)
    Abstract [en]

    In this work, we investigate the localization properties of a paradigmatic model, coupled to a monitoring environment and possessing a many-body localized (MBL) phase. We focus on the postselected no-click limit with quench random rates, i.e., random gains and losses. In this limit, the system is modeled by adding an imaginary random potential, rendering non-Hermiticity in the system. Numerically, we provide evidence that the system is localized for any finite amount of disorder. To analytically understand our results, we extend the quantum random energy model (QREM) to the non-Hermitian scenario. The Hermitian QREM has been used previously as a benchmark model for MBL. The QREM exhibits a size-dependent MBL transition, where the critical value scales as Wc∼LlnL with system size and presenting many-body mobility edges. We reveal that the non-Hermitian QREM with random gain-loss offers a significantly stronger form of localization, evident in the nature of the many-body mobility edges and the value for the transition, which scales as Wc∼ln1/2L with the system size.

  • 68.
    Delacretaz, Luca, V
    et al.
    Stanford Univ, Dept Phys, Stanford, CA 94305 USA..
    Gouteraux, Blaise
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Univ Paris Saclay, Ctr Theoret Phys, Ecole Polytech, CNRS UMR 7644, F-91128 Palaiseau, France.;Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Hartno, Sean A.
    Stanford Univ, Dept Phys, Stanford, CA 94305 USA.;SLAC Natl Accelerator Lab, Stanford Inst Mat & Energy Sci, 2575 Sand Hill Rd, Menlo Pk, CA 94025 USA..
    Karlsson, Anna
    Princeton Univ Sch Nat Sci, Inst Adv Study, 1 Einstein Dr, Princeton, NJ 08540 USA.;Chalmers Univ Technol, Dept Phys, Div Theoret Phys, SE-41296 Gothenburg, Sweden..
    Theory of collective magnetophonon resonance and melting of a field-induced Wigner solid2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 8, article id 085140Article in journal (Refereed)
    Abstract [en]

    Electron solid phases of matter are revealed by characteristic vibrational resonances. Sufficiently large magnetic fields can overcome the effects of disorder, leading to a weakly pinned collective mode called the magnetophonon. Consequently, in this regime it is possible to develop a tightly constrained hydrodynamic theory of pinned magnetophonons. The behavior of the magnetophonon resonance across thermal and quantum melting transitions has been experimentally characterized in two-dimensional electron systems. Applying our theory to these transitions we explain several key features of the data. Firstly, violation of the Fukuyama-Lee sum rule as the transition is approached is shown to be a consequence of the non-Lorentzian form taken by the resonance. Secondly, this non-Lorentzian shape is shown to be caused by dissipative channels that become especially important close to melting: proliferating dislocations and uncondensed charge carriers.

  • 69. Delacretaz, Luca V.
    et al.
    Goutéraux, Blaise
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stanford University, United States.
    Hartnoll, Sean A.
    Karlsson, Anna
    Theory of hydrodynamic transport in fluctuating electronic charge density wave states2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 19, article id 195128Article in journal (Refereed)
    Abstract [en]

    We describe the collective hydrodynamic motion of an incommensurate charge density wave state in a clean electronic system. Our description simultaneously incorporates the effects of both pinning due to weak disorder and also phase relaxation due to proliferating dislocations. We show that the interplay between these two phenomena has important consequences for charge and momentum transport. For instance, it can lead to metal-insulator transitions. We furthermore identify signatures of fluctuating density waves in frequency and spatially resolved conductivities. Phase disordering is well known to lead to a large viscosity. We derive a precise formula for the phase relaxation rate in terms of the viscosity in the dislocation cores. We thereby determine the viscosity of the superconducting state of BSCCO from the observed melting dynamics of Abrikosov lattices and show that the result is consistent with dissipation into Bogoliubov quasiparticles.

  • 70.
    Deng, Xiaolong
    et al.
    Leibniz-Rechenzentrum, Boltzmannstr. 1, D-85748 Garching bei München, Germany, Boltzmannstr. 1.
    Khaymovich, Ivan M.
    Nordita SU.
    Burin, Alexander L.
    Department of Chemistry, School of Science & Engineering, https://ror.org/04vmvtb21 Tulane University, New Orleans, Louisiana 70118, USA.
    Superdiffusion in a random two-dimensional system with time-reversal symmetry and long-range hopping2024In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 109, no 17, article id 174208Article in journal (Refereed)
    Abstract [en]

    Although it is recognized that Anderson localization takes place for all states at a dimension d less than or equal to 2, while delocalization is expected for hopping V(r) decreasing with the distance slower or as r-d, the localization problem in the crossover regime for the dimension d=2 and hopping V(r)â r-2 is not resolved yet. Following earlier suggestions we show that for the hopping determined by two-dimensional anisotropic dipole-dipole interactions in the presence of time-reversal symmetry there exist two distinguishable phases at weak and strong disorder. The first phase is characterized by ergodic dynamics and superdiffusive transport, while the second phase is characterized by diffusive transport and delocalized eigenstates with fractal dimension less than 2. The transition between phases is resolved analytically using the extension of scaling theory of localization and verified numerically using an exact numerical diagonalization.

  • 71.
    Dong, Zhihua
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Schönecker, Stephan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Chen, Dengfu
    Li, Wei
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Long, Mujun
    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, Uppsala, Sweden; Research Institute for Solid State Physics and Optics, Wigner Research Center for Physics, Budapest, Hungary.
    Elastic properties of paramagnetic austenitic steel at finite temperature: Longitudinal spin fluctuations in multicomponent alloys2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 17, article id 174415Article in journal (Refereed)
    Abstract [en]

    We propose a first-principles framework for longitudinal spin fluctuations (LSFs) in disordered paramagnetic (PM) multicomponent alloy systems and apply it to investigate the influence of LSFs on the temperature dependence of two elastic constants of PM austenitic stainless steel Fe15Cr15Ni. The magnetic model considers individual fluctuating moments in a static PM medium with first-principles-derived LSF energetics in conjunction with describing chemical disorder and randomness of the transverse magnetic component in the single-site alloy formalism and disordered local moment (DLM) picture. A temperature-sensitive mean magnetic moment is adopted to accurately represent the LSF state in the elastic-constant calculations. We make evident that magnetic interactions between an LSF impurity and the PM medium are weak in the present steel alloy. This allows gaining accurate LSF energetics and mean magnetic moments already through a perturbation from the static DLM moments instead of a tedious self-consistent procedure. We find that LSFs systematically lower the cubic shear elastic constants c' and c(44) by similar to 6 GPa in the temperature interval 300-1600 K, whereas the predominant mechanism for the softening of both elastic constants with temperature is the magneto-volume coupling due to thermal lattice expansion. We find that non-negligible local magnetic moments of Cr and Ni are thermally induced by LSFs, but they exert only a small influence on the elastic properties. The proposed framework exhibits high flexibility in accurately accounting for finite-temperature magnetism and its impact on the mechanical properties of PM multicomponent alloys.

  • 72.
    Dornheim, Tobias
    et al.
    Ctr Adv Syst Understanding CASUS, D-02826 Gorlitz, Germany.;Helmholtz Zentrum Dresden Rossendorf HZDR, D-01328 Dresden, Germany..
    Moldabekov, Zhandos A.
    Ctr Adv Syst Understanding CASUS, D-02826 Gorlitz, Germany.;Helmholtz Zentrum Dresden Rossendorf HZDR, D-01328 Dresden, Germany..
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Space and Plasma Physics.
    Analytical representation of the local field correction of the uniform electron gas within the effective static approximation2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, no 16, article id 165102Article in journal (Refereed)
    Abstract [en]

    The description of electronic exchange-correlation effects is of paramount importance for many applications in physics, chemistry, and beyond. In a recent paper, Dornheim et al. [Phys. Rev. Lett. 125, 235001 (2020)] have presented the effective static approximation (ESA) to the local field correction (LFC), which allows for the highly accurate estimation of electronic properties such as the interaction energy and the static structure factor. In this work, we give an analytical parametrization of the LFC within ESA that is valid for any wave number, and available for the entire range of densities (0.7 <= r(s) <= 20) and temperatures (0 <= theta <= 4) that are relevant for applications both in the ground state and in the warm dense matter regime. A short implementation in PYTHON is provided, which can easily be incorporated into existing codes. In addition, we present an extensive analysis of the performance of ESA regarding the estimation of various quantities like the dynamic structure factor, static dielectric function, the electronically screened ion potential, and also the stopping power in an electronic medium. In summary, we find that the ESA gives an excellent description of all these quantities in the warm dense matter regime, and only becomes inaccurate when the electrons start to form a strongly correlated electron liquid (r(s) similar to 20). Moreover, we note that the exact incorporation of exact asymptotic limits often leads to a superior accuracy compared to the neural-net representation of the static LFC [T. Dornheim et al., J. Chem. Phys. 151, 194104 (2019)].

  • 73.
    Dornheim, Tobias
    et al.
    Ctr Adv Syst Understanding CASUS, D-02826 Gorlitz, Germany.;Helmholtz Zentrum Dresden Rossendorf HZDR, D-01328 Dresden, Germany..
    Wicaksono, Damar C.
    Ctr Adv Syst Understanding CASUS, D-02826 Gorlitz, Germany.;Helmholtz Zentrum Dresden Rossendorf HZDR, D-01328 Dresden, Germany..
    Suarez-Cardona, Juan E.
    Ctr Adv Syst Understanding CASUS, D-02826 Gorlitz, Germany.;Helmholtz Zentrum Dresden Rossendorf HZDR, D-01328 Dresden, Germany.;Tech Univ Dresden, D-01062 Dresden, Germany..
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Space and Plasma Physics.
    Boehme, Maximilian P.
    Ctr Adv Syst Understanding CASUS, D-02826 Gorlitz, Germany.;Helmholtz Zentrum Dresden Rossendorf HZDR, D-01328 Dresden, Germany.;Tech Univ Dresden, D-01062 Dresden, Germany..
    Moldabekov, Zhandos A.
    Ctr Adv Syst Understanding CASUS, D-02826 Gorlitz, Germany.;Helmholtz Zentrum Dresden Rossendorf HZDR, D-01328 Dresden, Germany..
    Hecht, Michael
    Ctr Adv Syst Understanding CASUS, D-02826 Gorlitz, Germany.;Helmholtz Zentrum Dresden Rossendorf HZDR, D-01328 Dresden, Germany..
    Vorberger, Jan
    Helmholtz Zentrum Dresden Rossendorf HZDR, D-01328 Dresden, Germany..
    Extraction of the frequency moments of spectral densities from imaginary-time correlation function data2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 107, no 15, article id 155148Article in journal (Refereed)
    Abstract [en]

    We introduce an exact framework to compute the positive frequency moments M(alpha)(q) = (omega alpha) of different dynamic properties from imaginary-time quantum Monte Carlo data. As a practical example, we obtain the first five moments of the dynamic structure factor S(q, omega) of the uniform electron gas at the electronic Fermi temperature based on ab initio path integral Monte Carlo simulations. We find excellent agreement with known sum rules for alpha = 1, 3, and present results for alpha = 2, 4, 5. Our idea can be straightforwardly generalized to other dynamic properties such as the single-particle spectral function A(q, omega), and will be useful for a number of applications, including the study of ultracold atoms, exotic warm dense matter, and condensed matter systems.

  • 74.
    Duan, Yu-Xia
    et al.
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Zhang, Cheng
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Rusz, Jan
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Oppeneer, Peter M.
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden..
    Durakiewicz, Tomasz
    Marie Curie Sklodowska Univ, Lnstitute Phys, PL-20031 Lublin, Poland..
    Sassa, Yasmine
    Uppsala Univ, Dept Phys & Astron, Box 516, S-75120 Uppsala, Sweden.;Chalmers Univ Technol, Dept Phys, S-41296 Gothenburg, Sweden..
    Tjernberg, Oscar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Berntsen, Magnus H.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Wu, Fan-Ying
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Zhao, Yin-Zou
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Song, Jiao-Jiao
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Wu, Qi-Yi
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Luo, Yang
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China..
    Bauer, Eric D.
    Los Alamos Natl Lab, Condensed Matter & Magnet Sci Grp, Los Alamos, NM 87545 USA..
    Thompson, Joe D.
    Los Alamos Natl Lab, Condensed Matter & Magnet Sci Grp, Los Alamos, NM 87545 USA..
    Meng, Jian-Qiao
    Cent S Univ, Sch Phys & Elect, Changsha 410083, Hunan, Peoples R China.;Hunan Normal Univ, SICQEA, Changsha 410081, Hunan, Peoples R China..
    Crystal electric field splitting and f-electron hybridization in heavy-fermion CePt2In72019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 8, article id 085141Article in journal (Refereed)
    Abstract [en]

    We use high-resolution angle-resolved photoemission spectroscopy to investigate the electronic structure of the antiferromagnetic heavy fermion compound CePt2In7, which is amember of the CeIn3-derived heavy fermion material family. Weak hybridization among 4f electron states and conduction bands was identified in CePt2In7 at low temperature much weaker than that in the other heavy fermion compounds like CeIrIn5 and CeRhIn5. The Ce 4f spectrum shows fine structures near the Fermi energy, reflecting the crystal electric field splitting of the 4f(5/2)(1) and 4f(7/2)(1) states. Also, we find that the Fermi surface has a strongly three-dimensional topology, in agreement with density-functional theory calculations.

  • 75. Dufouleur, J.
    et al.
    Xypakis, E.
    Buechner, B.
    Giraud, R.
    Bardarson, Jens Hjörleifur
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory. Max Planck Institute for Physics - Max-Planck-Gesellschaft, Germany.
    Suppression of scattering in quantum confined 2D helical Dirac systems2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 7, article id 075401Article in journal (Refereed)
    Abstract [en]

    Transport properties of helical Dirac fermions in disordered quantum wires are investigated in the large energy limit. In the quasiballistic regime, the conductance and the Fano factor are sensitive to disorder only when the Fermi energy is close to an opening of a transverse mode. In the limit of a large number of transverse modes, transport properties are insensitive to the geometry of the nanowire or the nature and strength of the disorder but, instead, are dominated by the properties of the interface between the ohmic contact and the nanowire. In the case of a heavily doped Dirac metallic contact, the conductance is proportional to the energy with an average transmission T = pi/4 and a Fano factor of F similar or equal to 0.13. Those results can be generalized to a much broader class of contacts, the exact values of T and F depending on the model used for the contacts. The energy dependence of Aharonov-Bohm oscillations is determined, revealing a damped oscillatory behavior and phase shifts due to the one-dimensional subband quantization and which are not the signature of the nontrivial topology.

  • 76.
    Dunnett, K.
    et al.
    Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Narayan, Awadhesh
    Swiss Fed Inst Technol, Mat Theory, Wolfgang Pauli Str 27, CH-8093 Zurich, Switzerland..
    Spaldin, N. A.
    Swiss Fed Inst Technol, Mat Theory, Wolfgang Pauli Str 27, CH-8093 Zurich, Switzerland..
    Balatsky, Alexander
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden.;Los Alamos Natl Lab, Inst Mat Sci, Los Alamos, NM 87545 USA.;Univ Connecticut, Dept Phys, Storrs, CT 06269 USA..
    Strain and ferroelectric soft-mode induced superconductivity in strontium titanate2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 14, article id 144506Article in journal (Refereed)
    Abstract [en]

    We investigate the effects of strain on superconductivity with particular reference to SrTiO3. Assuming that a ferroelectric mode that softens under tensile strain is responsible for the coupling, an increase in the critical temperature and range of carrier densities for superconductivity is predicted, while the peak of the superconducting dome shifts towards lower carrier densities. Using a Ginzburg-Landau approach in 2D, we find a linear dependence of the critical temperature on strain: if the couplings between the order parameter and strains in different directions differ while their sum is fixed, different behaviors under uniaxial and biaxial strain can be understood.

  • 77.
    Dunnett, Kirsty
    et al.
    Nordita SU;Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden..
    Ferrier, A.
    UCL, Dept Phys & Astron, Gower St, London WC1E 6BT, England..
    Zamora, A.
    UCL, Dept Phys & Astron, Gower St, London WC1E 6BT, England..
    Dagvadorj, G.
    UCL, Dept Phys & Astron, Gower St, London WC1E 6BT, England.;Univ Warwick, Dept Phys, Coventry CV4 7AL, W Midlands, England..
    Szymanska, M. H.
    UCL, Dept Phys & Astron, Gower St, London WC1E 6BT, England..
    Properties of the signal mode in the polariton optical parametric oscillator regime2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 16, article id 165307Article in journal (Refereed)
    Abstract [en]

    Theoretical analyses of the polariton optical parametric oscillator (OPO) regime often rely on a mean-field approach based on the complex Gross-Pitaevskii equations in a three-mode approximation, where only three momentum states, the signal, pump, and idler, are assumed to be significantly occupied. This approximation, however, lacks a constraint to uniquely determine the signal and idler momenta. In contrast, multimode numerical simulations and experiments show a unique momentum structure for the OPO states. In this work we show that an estimate for the signal momentum chosen by the system can be found from a simple analysis of the pump-only configuration. We use this estimate to investigate how the chosen signal momentum depends on the properties of the drive.

  • 78. Durrenfeld, Philipp
    et al.
    Xu, Yongbing
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. Department of Physics, University of Gothenburg, .
    Zhou, Yan
    Controlled skyrmion nucleation in extended magnetic layers using a nanocontact geometry2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 5, article id 054430Article in journal (Refereed)
    Abstract [en]

    We propose and numerically simulate a spintronic device layout consisting of a nanocontact on top of an extended Co/Pt bilayer. The interfacial Dzyaloshinskii-Moriya interaction in such bilayer systems can lead to the possible existence of metastable skyrmions. A small dc current injected through the nanocontact enables the manipulation of the size as well as the annihilation of an initially present skyrmion, while ps-long current pulses allow for the controlled nucleation of single skyrmions underneath the nanocontact. The results are obtained from micromagnetic simulations and can be potentially used for future magnetic storage implementations.

  • 79.
    Edberg, Richard
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Bakke, I. M. B.
    Univ Oslo, Ctr Mat Sci & Nanotechnol, Dept Chem, N-0315 Oslo, Norway..
    Kondo, H.
    Kyushu Inst Technol, Fac Engn, Kitakyushu, Fukuoka 8048550, Japan..
    Sandberg, L. Orduk
    Univ Copenhagen, Niels Bohr Inst, DK-2100 Copenhagen, Denmark..
    Haubro, M. L.
    Univ Copenhagen, Niels Bohr Inst, DK-2100 Copenhagen, Denmark..
    Guthrie, M.
    European Spallat Source ERIC, S-22363 Lund, Sweden.;Univ Edinburgh, Sch Phys & Astron, Edinburgh EH9 3FD, Midlothian, Scotland.;Univ Edinburgh, Ctr Sci Extreme Condit, Edinburgh EH9 3FD, Midlothian, Scotland..
    Holmes, A. T.
    European Spallat Source ERIC, S-22363 Lund, Sweden..
    Engqvist, J.
    Lund Univ, Div Solid Mech, POB 118, SE-22100 Lund, Sweden..
    Wildes, A.
    Inst Laue Langevin, F-38042 Grenoble, France..
    Matsuhira, K.
    Kyushu Inst Technol, Fac Engn, Kitakyushu, Fukuoka 8048550, Japan..
    Lefmann, K.
    Univ Copenhagen, Niels Bohr Inst, DK-2100 Copenhagen, Denmark..
    Deen, P. P.
    Univ Copenhagen, Niels Bohr Inst, DK-2100 Copenhagen, Denmark.;European Spallat Source ERIC, S-22363 Lund, Sweden..
    Mito, M.
    Kyushu Inst Technol, Fac Engn, Kitakyushu, Fukuoka 8048550, Japan..
    Henelius, Patrik
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory. Abo Akad Univ, Fac Sci & Engn, Turku 20500, Finland..
    Effects of uniaxial pressure on the spin ice Ho2Ti2O72020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, no 18, article id 184408Article in journal (Refereed)
    Abstract [en]

    The spin ice materials Ho2Ti2O7 and Dy2Ti2O7 are experimental and theoretical exemplars of highly frustrated magnetic materials. However, the effects of applied uniaxial pressure are not well studied, and here we report magnetization measurements of Ho2Ti2O7 under uniaxial pressure applied in the [001], [111], and [110] crystalline directions. The basic features are captured by an extension of the dipolar spin ice model. We find a good match between our model and measurements with pressures applied along two of the three directions, and we extend the framework to discuss the influence of crystal misalignment for the third direction. The parameters determined from the magnetization measurements reproduce neutron scattering measurements that we perform under uniaxial pressure applied along the [110] crystalline direction. In the detailed analysis, we include the recently verified susceptibility dependence of the demagnetizing factor. Our work demonstrates the application of a moderate applied pressure to modify the magnetic interaction parameters. The knowledge can be used to predict critical pressures needed to induce new phases and transitions in frustrated materials, and in the case of Ho2Ti2O7 we expect a transition to a ferromagnetic ground state for uniaxial pressures above 3.3 GPa.

  • 80.
    Edberg, Richard
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Sandberg, L. Orduk
    Univ Copenhagen, Nanosci Ctr, Niels Bohr Inst, Univ Pk 5, DK-2100 Copenhagen O, Denmark..
    Bakke, I. M. Bergh
    Univ Oslo, Ctr Mat Sci & Nanotechnol, N-0315 Oslo, Norway..
    Haubro, M. L.
    Univ Copenhagen, Nanosci Ctr, Niels Bohr Inst, Univ Pk 5, DK-2100 Copenhagen O, Denmark..
    Folkers, L. C.
    Lund Univ, Dept Chem, Lund, Sweden..
    Mangin-Thro, L.
    Inst Laue Langevin, F-38042 Grenoble, France..
    Wildes, A.
    Inst Laue Langevin, F-38042 Grenoble, France..
    Zaharko, O.
    Paul Scherrer Inst, Lab Neutron Scattering, CH-5232 Villigen, Switzerland..
    Guthrie, M.
    European Spallat Source ERIC, S-22363 Lund, Sweden.;Univ Edinburgh, Sch Phys & Astron, Edinburgh, Midlothian, Scotland.;Univ Edinburgh, Ctr Sci Extreme Condit, Edinburgh, Midlothian, Scotland..
    Holmes, A. T.
    European Spallat Source ERIC, S-22363 Lund, Sweden..
    Sorby, M. H.
    Inst Energy Technol, Dept Neutron Mat Characterizat, POB 40, N-2027 Kjeller, Norway..
    Lefmann, K.
    Univ Copenhagen, Nanosci Ctr, Niels Bohr Inst, Univ Pk 5, DK-2100 Copenhagen O, Denmark..
    Deen, P. P.
    Univ Copenhagen, Nanosci Ctr, Niels Bohr Inst, Univ Pk 5, DK-2100 Copenhagen O, Denmark.;European Spallat Source ERIC, S-22363 Lund, Sweden..
    Henelius, Patrik
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory. Abo Akad Univ, Fac Sci & Engn, Turku, Finland..
    Dipolar spin ice under uniaxial pressure2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 14, article id 144436Article in journal (Refereed)
    Abstract [en]

    The magnetically frustrated spin ice family of materials is host to numerous exotic phenomena such as magnetic monopole excitations and macroscopic residual entropy extending to low temperature. A finite-temperature ordering transition in the absence of applied fields has not been experimentally observed in the classical spin ice materials Dy2Ti2O7 and Ho2Ti2O7. Such a transition could be induced by the application of pressure, and in this work we consider the effects of uniaxial pressure on classical spin ice systems. Theoretically, we find that the pressure-induced ordering transition in Dy2Ti2O7 is strongly affected by the dipolar interaction. We also report measurements of the neutron structure factor of Ho2Ti2O7 under pressure and compare the experimental results to the predictions of our theoretical model.

  • 81.
    Ehteshami, Hossein
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. National University of Science and Technology, Russia.
    Thermophysical properties of paramagnetic Fe from first principles2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 22, article id 224406Article in journal (Refereed)
    Abstract [en]

    A computationally efficient, yet general, free-energy modeling scheme is developed based on first-principles calculations. Finite-temperature disorder associated with the fast (electronic and magnetic) degrees of freedom is directly included in the electronic structure calculations, whereas the vibrational free energy is evaluated by a proposed model that uses elastic constants to calculate average sound velocity of the quasiharmonic Debye model. The proposed scheme is tested by calculating the lattice parameter, heat capacity, and single-crystal elastic constants of alpha-, gamma-, and delta-iron as functions of temperature in the range 1000-1800 K. The calculations accurately reproduce the well-established experimental data on thermal expansion and heat capacity of gamma- and delta-iron. Electronic and magnetic excitations are shown to account for about 20% of the heat capacity for the two phases. Nonphonon contributions to thermal expansion are 12% and 10% for alpha- and delta-Fe and about 30% for gamma-Fe. The elastic properties predicted by the model are in good agreement with those obtained in previous theoretical treatments of paramagnetic phases of iron, as well as with the bulk moduli derived from isothermal compressibility measurements [N. Tsujino et al., Earth Planet. Sci. Lett. 375, 244 (2013)]. Less agreement is found between theoretically calculated and experimentally derived single-crystal elastic constants of gamma- and delta-iron.

  • 82.
    Eklund, Anders J.
    et al.
    Univ Oslo, Dept Phys, Box 1048 Blindern, N-0316 Oslo, Norway..
    Dvornik, Mykola
    NanOsc AB, Electrum 205, S-16440 Kista, Sweden..
    Qejvanaj, Fatjon
    NanOsc AB, Electrum 205, S-16440 Kista, Sweden..
    Jiang, Sheng
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Chung, Sunjae
    Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden.;Korea Natl Univ Educ, Dept Phys Educ, Cheongju 28173, South Korea..
    Åkerman, Johan
    KTH, School of Engineering Sciences (SCI), Applied Physics. NanOsc AB, Electrum 205, S-16440 Kista, Sweden.
    Malm, Gunnar
    KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering.
    Impact of intragrain spin wave reflections on nanocontact spin torque oscillators2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, no 21, article id 214433Article in journal (Refereed)
    Abstract [en]

    We investigate the origin of the experimentally observed varying current-frequency nonlinearity of the propagating spin wave mode in nanocontact spin torque oscillators. Nominally identical devices with 100 nm diameter are characterized by electrical microwave measurements and show large variation in the generated frequency as a function of drive current. This quantitative and qualitative device-to-device variation is described in terms of continuous and discontinuous nonlinear transitions between linear current intervals. The thin-film grain microstructure in our samples is determined using atomic force and scanning electron microscopy to be on the scale of 30 nm. Micromagnetic simulations show that the reflection of spin waves against the grain boundaries results in standing wave resonance configurations. For a simulated device with a single artificial grain, the frequency increases linearly with the drive current until the decreased wavelength eventually forces another spin wave antinode to be formed. This transition results in a discontinuous step in the frequency versus current relation. Simulations of complete, randomly generated grain microstructures additionally shows continuous nonlinearity and a resulting device-to-device variation in frequency that is similar to the experimental levels. The impact of temperature from 4 to 300 K on the resonance mode-transition nonlinearity and frequency noise is investigated using simulations and it is found that the peak levels of the spectral linewidth as a function of drive current agree quantitatively with typical levels found in experiments at room temperature. The impact of the grain microstructure on the localized oscillation modes is also investigated.

  • 83. Ertan, Emelie
    et al.
    Kimberg, Victor
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Siberian Fed Univ, Russia.
    Gel'mukhanov, Faris
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Siberian Fed Univ, Russia.
    Hennies, Franz
    Rubensson, Jan-Erik
    Schmitt, Thorsten
    Strocov, Vladimir N.
    Zhou, Kejin
    Iannuzzi, Marcella
    Foehlisch, Alexander
    Odelius, Michael
    Pietzsch, Annette
    Theoretical simulations of oxygen K-edge resonant inelastic x-ray scattering of kaolinite2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 14, article id 144301Article in journal (Refereed)
    Abstract [en]

    Near-edge x-ray absorption fine structure (NEXAFS) and resonant inelastic x-ray scattering (RIXS) measurements at the oxygen K edge were combined with theoretical spectrum simulations, based on periodic density functional theory and nuclear quantum dynamics, to investigate the electronic structure and chemical bonding in kaolinite Al2Si2O5(OH)(4). We simulated NEXAFS spectra of all crystallographically inequivalent oxygen atoms in the crystal and RIXS spectra of the hydroxyl groups. Detailed insight into the ground-state potential energy surface of the electronic states involved in the RIXS process were accessed by analyzing the vibrational excitations, induced by the core excitation, in quasielastic scattering back to the electronic ground state. In particular, we find that the NEXAFS pre-edge is dominated by features related to OH groups within the silica and alumina sheets, and that the vibrational progression in RIXS can be used to selectively probe vibrational modes of this subclass of OH groups. The signal is dominated by the OH stretching mode, but also other lower vibrational degrees of freedom, mainly hindered rotational modes, contribute to the RIXS signal.

  • 84. Eschmann, Tim
    et al.
    Mishchenko, Petr A.
    O'Brien, Kevin
    Univ Cologne, Inst Theoret Phys, D-50937 Cologne, Germany..
    Bojesen, Troels A.
    Kato, Yasuyuki
    Hermanns, Maria
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Motome, Yukitoshi
    Trebst, Simon
    Thermodynamic classification of three-dimensional Kitaev spin liquids2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, no 7, article id 075125Article in journal (Refereed)
    Abstract [en]

    In the field of frustrated magnetism, Kitaev models provide a unique framework to study the phenomena of spin fractionalization and emergent lattice gauge theories in two and three spatial dimensions. Their ground states are quantum spin liquids, which can typically be described in terms of a Majorana band structure and an ordering of the underlying Z(2) gauge structure. Here we provide a comprehensive classification of the "gauge physics" of a family of elementary three-dimensional Kitaev models, discussing how their thermodynamics and ground state order depends on the underlying lattice geometry. Using large-scale, sign-free quantum Monte Carlo simulations we show that the ground-state gauge order can generally be understood in terms of the length of elementary plaquettes-a result which extends the applicability of Lieb's theorem to lattice geometries beyond its original scope. At finite temperatures, the proliferation of (gapped) vison excitations destroys the gauge order at a critical temperature scale, which we show to correlate with the size of vison gap for the family of three-dimensional Kitaev models. We also discuss two notable exceptions where the lattice structure gives rise to "gauge frustration" or intertwines the gauge ordering with time-reversal symmetry breaking In a more general context, the thermodynamic gauge transitions in such 3D Kitaev models are one of the most natural settings for phase transitions beyond the standard Landau-Ginzburg-Wilson paradigm.

  • 85.
    Ferreiros, Yago
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Vozmediano, Maria A. H.
    Elastic gauge fields and Hall viscosity of Dirac magnons2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 5, article id 054404Article in journal (Refereed)
    Abstract [en]

    We analyze the coupling of elastic lattice deformations to the magnon degrees of freedom of magnon Dirac materials. For a honeycomb ferromagnet we find that, as happens in the case of graphene, elastic gauge fields appear coupled to the magnon pseudospinors. For deformations that induce constant pseudomagnetic fields, the spectrum around the Dirac nodes splits into pseudo-Landau levels. We show that when a Dzyaloshinskii-Moriya interaction is considered, a topological gap opens in the system and a Chern-Simons effective action for the elastic degrees of freedom is generated. Such a term encodes a phonon Hall viscosity response, entirely generated by quantum fluctuations of magnons living in the vicinity of the Dirac points. The magnon Hall viscosity vanishes at zero temperature, and grows as temperature is raised and the states around the Dirac points are increasingly populated.

  • 86.
    Ferreiros, Yago
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Zyuzin, A. A.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Bardarson, Jens H
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Anomalous Nernst and thermal Hall effects in tilted Weyl semimetals2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 11, article id 115202Article in journal (Refereed)
    Abstract [en]

    We study the anomalous Nernst and thermal Hall effects in a linearized low-energy model of a tilted Weyl semimetal, with two Weyl nodes separated in momentum space. For inversion symmetric tilt, we give analytic expressions in two opposite limits: For a small tilt, corresponding to a type-I Weyl semimetal, the Nernst conductivity is finite and independent of the Fermi level; for a large tilt, corresponding to a type-II Weyl semimetal, it acquires a contribution depending logarithmically on the Fermi energy. This result is in a sharp contrast to the nontilted case, where the Nernst response is known to be zero in the linear model. The thermal Hall conductivity similarly acquires Fermi surface contributions, which add to the Fermi level-independent, zero-tilt result, and is suppressed as one over the tilt parameter at half filling in the type-II phase. In the case of inversion-breaking tilt, with the tilting vector of equal modulus in the two Weyl cones, all Fermi surface contributions to both anomalous responses cancel out, resulting in zero Nernst conductivity. We discuss two possible experimental setups, representing open and closed thermoelectric circuits.

  • 87.
    Fleckenstein, Christoph
    et al.
    KTH, School of Engineering Sciences (SCI), Physics. Univ Wurzburg, D-97074 Wurzburg, Germany.;KTH Royal Inst Technol, Dept Phys, SE-10691 Stockholm, Sweden..
    Bukov, Marin
    Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA.;St Kliment Ohridski Univ Sofia, Dept Phys, 5 James Bourchier Blvd, Sofia 1164, Bulgaria..
    Prethermalization and thermalization in periodically driven many-body systems away from the high-frequency limit2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, no 14, article id L140302Article in journal (Refereed)
    Abstract [en]

    We investigate a class of periodically driven many-body systems that allows us to extend the phenomenon of prethermalization to the vicinity of isolated intermediate-to-low drive frequencies away from the high-frequency limit. We provide numerical evidence for the formation of a parametrically long-lived prethermal plateau, captured by an effective Floquet Hamiltonian computed using the replica inverse-frequency expansion, and demonstrate its stability with respect to random perturbations in the drive period. Considering exclusively nonintegrable Floquet Hamiltonians, we find that heating rates are nonuniversal: we observe Fermi's golden rule scaling, power-law scaling inconsistent with the golden rule, and non-power-law scaling, depending on the drive. Despite the asymptotic character of the inverse-frequency expansion, we show that it describes the thermostatic properties of the state all along the evolution up to infinite temperature, with higher-order terms improving the accuracy. Our results suggest a dynamical mechanism to gradually increase the temperature in isolated quantum simulators, such as ultracold atoms, and open up an alternative possibility to investigate thermal phase transitions and the interplay between thermal and quantum criticality using Floquet drives.

  • 88.
    Fleckenstein, Christoph
    et al.
    KTH, School of Engineering Sciences (SCI), Physics. Univ Wurzburg, D-97074 Wurzburg, Germany.;KTH Royal Inst Technol, Dept Phys, SE-10691 Stockholm, Sweden..
    Bukov, Marin
    Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA.;St Kliment Ohridski Univ Sofia, Dept Phys, 5 James Bourchier Blvd, Sofia 1164, Bulgaria..
    Thermalization and prethermalization in periodically kicked quantum spin chains2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, no 14, article id 144307Article in journal (Refereed)
    Abstract [en]

    We study the dynamics of periodically kicked many-body systems away from the high-frequency regime, and discuss a family of Floquet systems where the notion of prethermalization can be naturally extended to intermediate and low driving frequencies. We investigate numerically the dynamics of both integrable and nonintegrable systems, and report on the formation of a long-lived prethermal plateau, akin to the high-frequency limit, where the system thermalizes with respect to an effective Hamiltonian captured by the inverse-frequency expansion (IFE). Unlike the high-frequency regime, we find that the relevant heating times are model dependent: we analyze the stability of the prethermal plateau to small perturbations in the drive period and show that, in a spin chain whose IFE is intractable, the plateau duration is insensitive to the perturbation strength, in contrast to a chain where the IFE admits the resummation of an entire subseries. Infinitesimal perturbations are enough to restore the ergodic properties of the system, and decrease residual finite-size effects. Although the regime where the Floquet system leaves the prethermal plateau and starts heating up to infinite temperature is not captured by the IFE, we provide evidence that the evolved subsystem is described well by a thermal state with respect to the IFE Hamiltonian, with a gradually changing temperature, in accord with the eigenstate thermalization hypothesis.

  • 89.
    Fleckenstein, Christoph
    et al.
    KTH, School of Engineering Sciences (SCI), Physics. Univ Wurzburg, Inst Theoret Phys & Astrophys, D-97074 Wurzburg, Germany..
    Ziani, N. Traverso
    Univ Genoa, Dipartimento Fis, I-16146 Genoa, Italy.;CNR Spin, I-16146 Genoa, Italy..
    Calzona, A.
    Univ Wurzburg, Inst Theoret Phys & Astrophys, D-97074 Wurzburg, Germany..
    Sassetti, M.
    Univ Genoa, Dipartimento Fis, I-16146 Genoa, Italy.;CNR Spin, I-16146 Genoa, Italy..
    Trauzettel, B.
    Univ Wurzburg, Inst Theoret Phys & Astrophys, D-97074 Wurzburg, Germany.;Wurzburg Dresden Cluster Excellence Ct Qmat, Wurzburg, Germany..
    Formation and detection of Majorana modes in quantum spin Hall trenches2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, no 12, article id 125303Article in journal (Refereed)
    Abstract [en]

    We propose a novel realization for a topologically superconducting phase hosting Majorana zero modes on the basis of quantum spin Hall systems. Remarkably, our proposal is completely free of ferromagnets. Instead, we confine helical edge states around a narrow defect line of finite length in a two-dimensional topological insulator. We demonstrate the formation of a new topological regime, hosting protected Majorana modes in the presence of s-wave superconductivity and Zeeman coupling. Interestingly, when the system is weakly tunnel coupled to helical edge state reservoirs, a particular transport signature is associated with the presence of a non-Abelian Majorana zero mode.

  • 90.
    Flór, Ian Matthias
    et al.
    Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden, The Netherlands.
    Donís-Vela, A.
    Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden, The Netherlands.
    Beenakker, C. W.J.
    Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden, The Netherlands.
    Lemut, G.
    Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden, The Netherlands.
    Dynamical simulation of the injection of vortices into a Majorana edge mode2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, no 23, article id 235309Article in journal (Refereed)
    Abstract [en]

    The chiral edge modes of a topological superconductor can transport fermionic quasiparticles with Abelian exchange statistics, but they can also transport non-Abelian anyons: edge vortices bound to a π-phase domain wall that propagates along the boundary. A pair of such edge vortices is injected by the application of an h/2e flux bias over a Josephson junction. Existing descriptions of the injection process rely on the instantaneous scattering approximation of the adiabatic regime [Beenakker, Phys. Rev. Lett. 122, 146803 (2019)10.1103/PhysRevLett.122.146803], where the internal dynamics of the Josephson junction is ignored. Here, we go beyond that approximation in a time-dependent many-body simulation of the injection process, followed by a braiding of mobile edge vortices with a pair of immobile Abrikosov vortices in the bulk of the superconductor. Our simulation sheds light on the properties of the Josephson junction needed for a successful implementation of a flying topological qubit.

  • 91.
    Forslund, Axel
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures. Mat Ctr Leoben Forsch GmbH, A-8700 Leoben, Austria..
    Ab initio surface free energies of tungsten with full account of thermal excitations2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 105, no 4, article id 045403Article in journal (Refereed)
    Abstract [en]

    The surface free energies of seven different facets of tungsten (W) are obtained up to the melting point with full account of all the relevant thermal excitations; in particular, thermal atomic vibrations, electronic excitations, and their mutual coupling. The latter is done using ab initio molecular dynamics simulations coupled with the thermodynamic integration technique. In this way, the calculations contain almost no error but the one related to the used exchange-correlation functional, which makes the results truly first principles. The obtained results are compared with previous quasiharmonic calculations for the surface free energies of W and experimental data. The anharmonic contribution is, as expected, important for open surfaces at high temperatures, which leads to a temperature dependence of the surface energy anisotropy. The calculated Wulff shapes and surface energies are in excellent agreement with experimental data close to the melting point, where the crystalline structure of the surface layers is destroyed by a dramatic mobility of the atoms there.

  • 92.
    Forslund, Axel
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures.
    Zhang, Xi
    Univ Stuttgart, Inst Mat Sci, Pfaffenwaldring 55, D-70569 Stuttgart, Germany..
    Grabowski, Blazej
    Univ Stuttgart, Inst Mat Sci, Pfaffenwaldring 55, D-70569 Stuttgart, Germany..
    Shapeev, Alexander, V
    Skolkovo Innovat Ctr, Skolkovo Inst Sci & Technol, Nobel St 3, Moscow 143026, Russia..
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Structures. Mat Ctr Leoben Forsch GmbH, A-8700 Leoben, Austria..
    Ab initio simulations of the surface free energy of TiN(001)2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, no 19, article id 195428Article in journal (Refereed)
    Abstract [en]

    The temperature dependence of the surface free energy of the industrially important TiN(001) system has been investigated by means of an extended two-stage upsampled thermodynamic integration using Langevin dynamics (TU-TILD) methodology, to include the fully anharmonic vibrational contribution, as obtained from ab initio molecular dynamics (AIMD). Inclusion of the fully anharmonic behavior is crucial, since the standard low-temperature quasiharmonic approximation exhibits a severe divergence in the surface free energy due to a high-temperature dynamical instability. The anharmonic vibrations compensate for the quasiharmonic divergence and lead to a modest overall temperature effect on the TiN(001) surface free energy, changing it from around 78 meV angstrom(-2) at 0 K to 73 meV angstrom(-2) at 3000 K. The statistical convergence of the molecular dynamics is facilitated by the use of machine-learning potentials, specifically moment tensor potentials, fitted for TiN(001) at finite temperature. The surface free energy obtained directly from the fitted machine-learning potentials is close to that obtained from the full AIMD simulations.

  • 93.
    Forslund, Ola Kenji
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Ohta, Hiroto
    Kyoto Univ, Engn Educ Res Ctr, Grad Sch Engn, Kyoto 6158530, Japan.;Kyoto Univ, Grad Sch Sci, Dept Chem, Kyoto 6068502, Japan..
    Kamazawa, Kazuya
    CROSS Neutron Sci & Technol Ctr, Tokai, Ibaraki 3191106, Japan..
    Stubbs, Scott L.
    Univ British Columbia, Dept Phys & Astron, Vancouver, BC V6T 1Z1, Canada..
    Ofer, Oren
    TRIUMF, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada..
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Michioka, Chishiro
    Kyoto Univ, Grad Sch Sci, Dept Chem, Kyoto 6068502, Japan..
    Yoshimura, Kazuyoshi
    Kyoto Univ, Grad Sch Sci, Dept Chem, Kyoto 6068502, Japan..
    Hitti, Bassam
    TRIUMF, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada..
    Arseneau, Donald
    TRIUMF, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada..
    Morris, Gerald D.
    TRIUMF, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada..
    Ansaldo, Eduardo J.
    Univ Saskatchewan, Dept Phys & Engn Phys, Saskatoon, SK S7N 5E2, Canada..
    Brewer, Jess H.
    Univ British Columbia, Dept Phys & Astron, Vancouver, BC V6T 1Z1, Canada.;TRIUMF, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada..
    Sugiyama, Jun
    CROSS Neutron Sci & Technol Ctr, Tokai, Ibaraki 3191106, Japan.;Japan Atom Energy Agcy, Adv Sci Res Ctr, Tokai, Ibaraki 3191195, Japan.;High Energy Accelerator Res Org, KEK, Tokai, Ibaraki 3191106, Japan..
    Revisiting the A-type antiferromagnet NaNiO2 with muon spin rotation measurements and density functional theory calculations2020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, no 18, article id 184412Article in journal (Refereed)
    Abstract [en]

    An A-type antiferromagnet, NaNiO2, was examined by means of positive muon spin rotation and relaxation (mu+SR) measurements and first-principles calculations based on a density functional theory (DFT). Below T-N = 20 K, a clear muon spin precession signal was observed in the mu+SR time spectrum recorded under zero field, due to the formation of a static internal magnetic field. The microscopic origin of such an internal field was computed as a sum of dipolar and hyperfine contact fields at the site (0.624, 0, 0.854), where both the muon site and the local spin density at such a site were predicted with DFT calculations. While the computed values were consistent with experimentally obtained ones, in both the antiferromagnetic and the paramagnetic states, the contribution of the hyperfine contact field was shown to be insignificant even below T-N. Finally, measurements at higher temperatures signified thermally activated Na-ion diffusion with E-a = 50(20) meV and D-Na(300K) = 8.8 x 10(-11) cm(2)/s, commonly observed in layered-type compounds.

  • 94.
    Forslund, Ola Kenji
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Papadopoulos, Konstantinos
    Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden..
    Nocerino, Elisabetta
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Morris, Gerald
    TRIUMF, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada..
    Hitti, Bassam
    TRIUMF, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada..
    Arseneau, Donald
    TRIUMF, 4004 Wesbrook Mall, Vancouver, BC V6T 2A3, Canada..
    Pomjakushin, Vladimir
    Paul Scherrer Inst, Lab Neutron Scattering & Imaging, CH-5232 Villigen, Switzerland..
    Matsubara, Nami
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Orain, Jean-Christophe
    Paul Scherrer Inst, Lab Muon Spin Spect, CH-5232 Villigen, Switzerland..
    Svedlindh, Peter
    Uppsala Univ, Dept Mat Sci & Engn, Box 35, SE-75103 Uppsala, Sweden..
    Andreica, Daniel
    Babes Bolyai Univ, Fac Phys, Cluj Napoca 400084, Romania..
    Jana, Somnath
    Indian Assoc Cultivat Sci, Ctr Adv Mat, Kolkata 700032, India..
    Sugiyama, Jun
    Comprehens Res Org Sci & Soc CROSS, Neutron Sci & Technol Ctr, Tokai, Ibaraki 3191106, Japan..
    Månsson, Martin
    KTH, School of Engineering Sciences (SCI), Applied Physics, Materials and Nanophysics.
    Sassa, Yasmine
    Chalmers Univ Technol, Dept Phys, SE-41296 Gothenburg, Sweden..
    Intertwined magnetic sublattices in the double perovskite compound LaSrNiReO62020In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 102, no 14, article id 144409Article in journal (Refereed)
    Abstract [en]

    We report a muon spin rotation (mu+SR) study of the magnetic properties of the double perovskite compound LaSrNiReO6. Using the unique length and time scales of the mu+SR technique, we successfully clarify the magnetic ground state of LaSrNiReO6, which was previously deemed as a spin glass state. Instead, our mu+SR results point toward a long-range dynamically ordered ground state below T-C = 23 K, for which a static limit is foreseen at T = 0. Furthermore, between 23 K < T <= 300 K, three different magnetic phases are identified: a dense (23 K < T < 75 K), a dilute (75 K <= T <= 250 K), and a paramagnetic (T > 250 K) state. Our results reveal how two separate yet intertwined magnetic lattices interact within the unique double perovskite structure and the importance of using complementary experimental techniques to obtain a complete understanding of the microscopic magnetic properties of complex materials.

  • 95. Franco, A. F.
    et al.
    Gonzalez-Fuentes, C.
    Åkerman, Johan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Garcia, C.
    Anisotropy constant and exchange coupling strength of perpendicularly magnetized CoFeB/Pd multilayers and exchange springs2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 14, article id 144417Article in journal (Refereed)
    Abstract [en]

    A model describing the ferromagnetic resonance of multilayer structures is used to characterize the interface anisotropy constant and interlayer exchange coupling strength associated to individual components of [CoFeB/Pd](n) multilayers with perpendicular magnetic anisotropy and [CoFeB/Pd](5)/(CoFeB or Co) exchange spring structures by comparing with ferromagnetic resonance behavior measurements. We find that the effective perpendicular anisotropy increases with the number of repetitions of the multilayer, which we could explain only after accounting for a different anisotropy at the bottom repetition of the multilayer with perpendicular anisotropy. Similarly, the characterization of the exchange coupling in our structures was only possible after accounting for individual components, thus portraying the importance of using a multilayer model to properly describe the magnetic behavior and properties of a multilayer structure. We find that the perpendicular anisotropy constant in amorphous Pd/CoFeB/Pd structures increases slightly from 0.295 to 0.315 mJ/m(2) when increasing the thickness of the CoFeB from 3 to 4 angstrom. Furthermore, we find that the exchange coupling in CoFeB/Pd(10 A degrees)/CoFeB structures decreases from 4.899 to 3.268 mJ/m(2) when increasing the thickness of the CoFeB from 3 to 4 angstrom. Finally, we find that the magnitude of the anisotropy at Co/Pd interfaces is 65% larger than at CoFeB/Pd interfaces, and the exchange coupling at CoFeB/Pd/Co interfaces decreases approximately 30% when compared to a CoFeB/Pd/CoFeB structure.

  • 96.
    Frank, Marius S.
    et al.
    Aarhus Univ, Dept Phys & Astron, DK-8000 Aarhus C, Denmark..
    Lee, Tsung-Han
    Rutgers State Univ, Phys & Astron Dept, Piscataway, NJ 08854 USA..
    Bhattacharyya, Gargee
    Aarhus Univ, Dept Phys & Astron, DK-8000 Aarhus C, Denmark..
    Tsang, Pak Ki Henry
    Florida State Univ, Dept Phys, Tallahassee, FL 32306 USA.;Florida State Univ, Natl High Magnet Field Lab, Tallahassee, FL 32306 USA..
    Quito, Victor L.
    Florida State Univ, Dept Phys, Tallahassee, FL 32306 USA.;Florida State Univ, Natl High Magnet Field Lab, Tallahassee, FL 32306 USA.;Iowa State Univ, Dept Phys & Astron, Ames, IA 50011 USA..
    Dobrosavljevic, Vladimir
    Florida State Univ, Dept Phys, Tallahassee, FL 32306 USA.;Florida State Univ, Natl High Magnet Field Lab, Tallahassee, FL 32306 USA..
    Christiansen, Ove
    Aarhus Univ, Dept Chem, DK-8000 Aarhus C, Denmark..
    Lanata, Nicola
    Aarhus Univ, Dept Phys & Astron, DK-8000 Aarhus C, Denmark.;Nordita SU.
    Quantum embedding description of the Anderson lattice model with the ghost Gutzwiller approximation2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 104, no 8, article id L081103Article in journal (Refereed)
    Abstract [en]

    We present benchmark calculations of the Anderson lattice model based on the recently developed "ghost Gutzwiller approximation". Our analysis shows that, in some parameters regimes, the predictions of the standard Gutzwiller approximation can be incorrect by orders of magnitude for this model. We show that this is caused by the inability of this method to describe simultaneously the Mott physics and the hybridization between correlated and itinerant degrees of freedom-whose interplay often governs the metal-insulator transition in real materials. Finally, we show that the ghost Gutzwiller approximation solves this problem, providing us with results in remarkable agreement with dynamical mean-field theory throughout the entire phase diagram, while being much less computationally demanding. We provide an analytical explanation of these findings and discuss their implications within the context of ab-initio computation of strongly correlated matter.

  • 97.
    Franklin, J.
    et al.
    Univ Connecticut, Dept Phys, Storrs, CT 06269 USA..
    Xu, B.
    Univ Connecticut, Dept Phys, Storrs, CT 06269 USA..
    Davino, D.
    Univ Connecticut, Dept Phys, Storrs, CT 06269 USA..
    Mahabir, A.
    Univ Connecticut, Dept Phys, Storrs, CT 06269 USA..
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Aschauer, U.
    Univ Bern, Dept Chem & Biochem, Bern, Switzerland..
    Sochnikov, I
    Univ Connecticut, Dept Phys, Storrs, CT 06269 USA.;Univ Connecticut, Inst Mat Sci, Storrs, CT 06269 USA..
    Giant Gruneisen parameter in a superconducting quantum paraelectric2021In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 103, no 21, article id 214511Article in journal (Refereed)
    Abstract [en]

    Superconductivity and ferroelectricity are typically thought of as incompatible because the former needs free carriers, but the latter is usually suppressed by free carriers. This is unless the carrier concentration is sufficiently low to allow for polar distortions and mobile electrons to cooperate. In the case of strontium titanate with low carrier concentration, superconductivity and ferroelectricity have been shown to be correlated via various tuning methods, such as strain. Here, we report theoretically and experimentally evaluated Gruneisen parameters whose divergent giant values under tensile stress indicate that the dominant phonon mode which enhances the superconducting order is the ferroelectric transverse soft phonon mode. This finding puts strong constraints on other phonon modes as the main contributors to the enhanced superconductivity in strained strontium titanate. The methodology shown here can be applied to strain tune and probe properties of other materials with polar distortions including topologically nontrivial ones.

  • 98.
    Fu, Ying
    et al.
    KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Jussi, Johnny Israelsson
    KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Elmlund, Louise
    Swedish Natl Forens Ctr, SE-58194 Linkoping, Sweden..
    Dunne, Simon
    Swedish Natl Forens Ctr, SE-58194 Linkoping, Sweden..
    Wang, Qin
    RISE Res Inst Sweden AB, Box 1070, SE-16425 Kista, Sweden..
    Brismar, Hjalmar
    KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, School of Engineering Sciences (SCI), Applied Physics.
    Intrinsic blinking characteristics of single colloidal CdSe-CdS/ZnS core-multishell quantum dots2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 3, article id 035404Article in journal (Refereed)
    Abstract [en]

    Fluorescence blinking of single colloidal semiconductor quantum dots (QDs) has been extensively studied, and several sophisticated models have been proposed. In this work, we derive Heisenberg equations of motion to carefully study principal transition processes, i.e., photoexcitation, energy relaxation, impact ionization and Auger recombination, radiative and nonradiative recombinations, and tunneling between core states and surface states, of the electron-hole pair in single CdSe-CdS/ZnS core-multishell QDs and show that the on-state probability density distribution of the QD fluorescence obeys the random telegraph signal theory because of the random radiative recombination of the photoexcited electron-hole pair in the QD core, while the off-state probability density distribution obeys the inverse power law distribution due to the series of random walks of the photoexcited electron in the two-dimensional surface-state network after the electron tunnels from the QD core to the QD surface. These two different blinking characteristics of the single QD are resolved experimentally by properly adjusting the optical excitation power and the bin time.

  • 99.
    Gani, Yohanes S.
    et al.
    Coll William & Mary, Dept Phys, Williamsburg, VA 23187 USA..
    Abergel, David
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, S-10691 Stockholm, Sweden.;Nat Phys, 4 Crinan St, London N1 9XW, England..
    Rossi, Enrico
    Coll William & Mary, Dept Phys, Williamsburg, VA 23187 USA..
    Electronic structure of graphene nanoribbons on hexagonal boron nitride2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 20, article id 205415Article in journal (Refereed)
    Abstract [en]

    Hexagonal boron nitride is an ideal dielectric to form two-dimensional heterostructures due to the fact that it can be exfoliated to be just a few atoms thick and its very low density of defects. By placing graphene nanoribbons on high quality hexagonal boron nitride it is possible to create ideal quasi-one-dimensional systems with very high mobility. The availability of high quality one-dimensional electronic systems is of great interest also given that when in proximity to a superconductor they can be effectively engineered to realize Majorana bound states. In this work we study how a boron nitride substrate affects the electronic properties of graphene nanoribbons. We consider both armchair and zigzag nanoribbons. Our results show that for some stacking configurations the boron nitride can significantly affect the electronic structure of the ribbons. In particular, for zigzag nanoribbons, due to the lock between spin and sublattice degree of freedom at the edges, the hexagonal boron nitride can induce a very strong spin splitting of the spin-polarized, edge states. We find that such spin splitting can be as high as 40 meV.

  • 100.
    Gao, Jun
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Khaymovich, Ivan M.
    Nordita SU; Institute for Physics of Microstructures, Russian Academy of Sciences, 603950 Nizhny Novgorod, GSP-105, Russia, GSP-105.
    Iovan, Adrian
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Wang, Xiao Wei
    Center for Integrated Quantum Information Technologies (IQIT), School of Physics and Astronomy and State Key Laboratory of Advanced Optical Communication Systems and Networks, Shanghai Jiao Tong University, Shanghai 200240, China.
    Krishna, Govind
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Xu, Ze Sheng
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Tortumlu, Emrah
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Balatsky, Alexander V.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Department of Physics, University of Connecticut, Storrs, Connecticut 06269, USA.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Elshaari, Ali W.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.
    Coexistence of extended and localized states in finite-sized mosaic Wannier-Stark lattices2023In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 108, no 14, article id L140202Article in journal (Refereed)
    Abstract [en]

    Quantum transport and localization are fundamental concepts in condensed matter physics. It is commonly believed that in one-dimensional systems, the existence of mobility edges is highly dependent on disorder. Recently, there has been a debate over the existence of an exact mobility edge in a modulated mosaic model without quenched disorder, the so-called mosaic Wannier-Stark lattice. Here, we experimentally implement such disorder-free mosaic photonic lattices using a silicon photonics platform. By creating a synthetic electric field, we could observe energy-dependent coexistence of both extended and localized states in a finite number of waveguides. The Wannier-Stark ladder emerges when the resulting potential is strong enough, and can be directly probed by exciting different spatial modes of the lattice. Our studies provide the experimental proof of coexisting sets of strongly localized and conducting (though weakly localized) states in finite-sized mosaic Wannier-Stark lattices, which hold the potential to encode high-dimensional quantum resources with compact and robust structures.

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