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  • 1.
    Banerjee, Saikat
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Interacting Dirac Matter2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The discovery of graphene in 2004 has led to a surge of activities focused on the theoretical and experimental studies of materials hosting linearly dispersive quasiparticles during the last decade. Rapid expansion in the list of materials having similar properties to graphene has led to the emergence of a new class of materials known as the Dirac materials. The low energy quasiparticles in this class of materials are described by a Dirac-like equation in contrast to the Schrödinger equation which governs the low energy dynamics in any conventional materials such as metals. The Dirac fermions, as we call these low-energy quasiparticles, in a wide range of materials ranging from the d-wave superconductors, graphene to the surface states of topological insulators share the common property. The particles move around as if they have lost their mass. This feature results in a completely new set of physical effects consisting of various transport and thermodynamic quantities, that are absent in conventional metals.

    This thesis is devoted to studying the properties of bosonic analogs of the commonly known Dirac materials where the quasiparticle are fermionic. In chapter one, we discuss the microscopic origin of the Dirac equation in several fermionic and bosonic systems. We observe identical features of the Dirac materials with quasiparticles of either statistics when the interparticle interaction is absent. Dirac materials with both types of quasiparticles possess the nodal excitations that are described by an effective Dirac-like equation. The possible physical effects due to the linear dispersions in fermionic and bosonic Dirac materials are also outlined.

    In chapter two, we propose a system of superconducting grains arranged in honeycomb lattice as a realization for Bosonic Dirac Materials (BDM). The underlying microscopic dynamics, which give rise to the emergence of Dirac structure in the spectrum of the collective phase oscillations, is discussed in detail. Similarities and differences of BDM systems to the conventional Dirac materials with fermionic quasiparticles are also mentioned. Chapter three is dedicated to the detailed analysis of the interaction effects on the stability and renormalization of the conical Dirac band structure. We find that the type of interaction dictates the possible fate of renormalized Dirac cone in both fermionic and bosonic Dirac materials. We study interaction effects in four different individual systems : (a) Dirac fermions in graphene interacting via Coulomb interactions, (b) Dirac fermions subjected to an onsite Hubbard repulsion, (c) Coulomb repulsion in charged Cooper pairs in honeycomb lattice and (d) Dirac magnons interacting via Heisenberg exchange interaction. The possibility of interaction induced gap opening at the Dirac nodal point described is also discussed in these cases.

    Chapter four mainly concerns the study of a related topic of the synthetic gauge fields. We discuss the possibility of Landau quantization in neutral particles. Possible experimental evidence in toroidal cold atomic traps is also mentioned. A connection to Landau levels in case of magnons is also described. We finally conclude our thesis in chapter five and discuss the possible future directions that can be taken as an extension for our works in interacting Dirac materials.

  • 2. Behrends, Jan
    et al.
    Bardarson, Jens H.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory. Max Planck Institute, Germany.
    Strongly angle-dependent magnetoresistance in Weyl semimetals with long-range disorder2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 6, article id 060201Article in journal (Refereed)
    Abstract [en]

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

  • 3. Behrends, Jan
    et al.
    Rhim, Jun-Won
    Liu, Shang
    Grushin, Adolfo G.
    Bardarson, Jens H.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory. Max-Planck-Institut für Physik Komplexer Systeme, Germany.
    Nodal-line semimetals from Weyl superlattices2017In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 96, no 24, article id 245101Article in journal (Refereed)
    Abstract [en]

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

  • 4.
    Belonoshko, Anatoly B.
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Lukinov, Timofei
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Condensed Matter Theory.
    Fu, Jie
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Zhao, Jijun
    Davis, Sergio
    Simak, Sergei I.
    Stabilization of body-centred cubic iron under inner-core conditions2017In: Nature Geoscience, ISSN 1752-0894, E-ISSN 1752-0908, Vol. 10, no 4, p. 312-+Article in journal (Refereed)
    Abstract [en]

    The Earth's solid core is mostly composed of iron. However, despite being central to our understanding of core properties, the stable phase of iron under inner-core conditions remains uncertain. The two leading candidates are hexagonal close-packed and body-centred cubic (bcc) crystal structures, but the dynamic and thermodynamic stability of bcc iron under inner-core conditions has been challenged. Here we demonstrate the stability of the bcc phase of iron under conditions consistent with the centre of the core using ab initio molecular dynamics simulations. We find that the bcc phase is stabilized at high temperatures by a diffusion mechanism that arises due to the dynamical instability of the phase at lower temperatures. On the basis of our simulations, we reinterpret experimental data as support for the stability of bcc iron under inner-core conditions. We suggest that the diffusion of iron atoms in solid state may explain both the anisotropy and the low shear modulus of the inner core.

  • 5. Bera, Soumya
    et al.
    Martynec, Thomas
    Schomerus, Henning
    Heidrich-Meisner, Fabian
    Hjörleifur Bardarson, Jens
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory. Max-Planck-Institut für Physik komplexer Systeme, Germany.
    One-particle density matrix characterization of many-body localization2017In: Annalen der Physik, ISSN 0003-3804, E-ISSN 1521-3889, Vol. 529, no 7, article id 1600356Article in journal (Refereed)
    Abstract [en]

    We study interacting fermions in one dimension subject to random, uncorrelated onsite disorder, a paradigmatic model of many-body localization (MBL). This model realizes an interaction-driven quantum phase transition between an ergodic and a many-body localized phase, with the transition occurring in the many-body eigenstates. We propose a single-particle framework to characterize these phases by the eigenstates (the natural orbitals) and the eigenvalues (the occupation spectrum) of the one-particle density matrix (OPDM) in individual many-body eigenstates. As a main result, we find that the natural orbitals are localized in the MBL phase, but delocalized in the ergodic phase. This qualitative change in these single-particle states is a many-body effect, since without interactions the single-particle energy eigenstates are all localized. The occupation spectrum in the ergodic phase is thermal in agreement with the eigenstate thermalization hypothesis, while in the MBL phase the occupations preserve a discontinuity at an emergent Fermi edge. This suggests that the MBL eigenstates are weakly dressed Slater determinants, with the eigenstates of the underlying Anderson problem as reference states. We discuss the statistical properties of the natural orbitals and of the occupation spectrum in the two phases and as the transition is approached. Our results are consistent with the existing picture of emergent integrability and localized integrals of motion, or quasiparticles, in the MBL phase. We emphasize the close analogy of the MBL phase to a zero-temperature Fermi liquid: in the studied model, the MBL phase is adiabatically connected to the Anderson insulator and the occupation-spectrum discontinuity directly indicates the presence of quasiparticles localized in real space. Finally, we show that the same picture emerges for interacting fermions in the presence of an experimentally-relevant bichromatic lattice and thereby demonstrate that our findings are not limited to a specific model.

  • 6.
    Bergqvist, Lars
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Eriksson, Olle
    Bergman, Anders
    Hellsvik, Johan
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Atomistic Spin Dynamics: Foundations and Applications2017Book (Other academic)
  • 7. Bovo, L.
    et al.
    Twengström, Mikael
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Petrenko, O. A.
    Fennell, T.
    Gingras, M. J. P.
    Bramwell, S. T.
    Henelius, P.
    Special temperatures in frustrated ferromagnets,Manuscript (preprint) (Other academic)
  • 8. 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.

  • 9. Erlingsson, Sigurdur I.
    et al.
    Manolescu, Andrei
    Nemnes, George Alexandru
    Bardarson, Jens H.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Sanchez, David
    Reversal of Thermoelectric Current in Tubular Nanowires2017In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 119, no 3, article id 036804Article in journal (Refereed)
    Abstract [en]

    We calculate the charge current generated by a temperature bias between the two ends of a tubular nanowire. We show that in the presence of a transversal magnetic field the current can change sign; i.e., electrons can either flow from the hot to the cold reservoir, or in the opposite direction, when the temperature bias increases. This behavior occurs when the magnetic field is sufficiently strong, such that Landau and snaking states are created, and the energy dispersion is nonmonotonic with respect to the longitudinal wave vector. The sign reversal can survive in the presence of impurities. We predict this result for core-shell nanowires, for uniform nanowires with surface states due to the Fermi level pinning, and for topological insulator nanowires.

  • 10.
    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.

  • 11.
    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.

  • 12. Fransson, J.
    et al.
    Thonig, D.
    Bessarab, P. F.
    Bhattacharjee, S.
    Hellsvik, Johan
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Nordström, L.
    Microscopic theory for coupled atomistic magnetization and lattice dynamics2017In: Physical Review Materials, ISSN 2475-9953, Vol. 1, no 7, article id 074404Article in journal (Refereed)
    Abstract [en]

    A coupled atomistic spin and lattice dynamics approach is developed which merges the dynamics of these two degrees of freedom into a single set of coupled equations of motion. The underlying microscopic model comprises local exchange interactions between the electron spin and magnetic moment and the local couplings between the electronic charge and lattice displacements. An effective action for the spin and lattice variables is constructed in which the interactions among the spin and lattice components are determined by the underlying electronic structure. In this way, expressions are obtained for the electronically mediated couplings between the spin and lattice degrees of freedom, besides the well known interatomic force constants and spin-spin interactions. These former susceptibilities provide an atomistic ab initio description for the coupled spin and lattice dynamics. It is important to notice that this theory is strictly bilinear in the spin and lattice variables and provides a minimal model for the coupled dynamics of these subsystems and that the two subsystems are treated on the same footing. Questions concerning time-reversal and inversion symmetry are rigorously addressed and it is shown how these aspects are absorbed in the tensor structure of the interaction fields. By means of these results regarding the spin-lattice coupling, simple explanations of ionic dimerization in double-antiferromagnetic materials, as well as charge density waves induced by a nonuniform spin structure, are given. In the final parts, coupled equations of motion for the combined spin and lattice dynamics are constructed, which subsequently can be reduced to a form which is analogous to the Landau-Lifshitz-Gilbert equations for spin dynamics and a damped driven mechanical oscillator for the ionic motion. It is important to notice, however, that these equations comprise contributions that couple these descriptions into one unified formulation. Finally, Kubo-like expressions for the discussed exchanges in terms of integrals over the electronic structure and, moreover, analogous expressions for the damping within and between the subsystems are provided. The proposed formalism and types of couplings enable a step forward in the microscopic first principles modeling of coupled spin and lattice quantities in a consistent format.

  • 13.
    Fu, Jie
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory. Ningbo Univ, Peoples R China; Dalian Univ Technol, Peoples R China.
    Zhao, Jijun
    Plyasunov, Andrey V.
    Belonoshko, Anatoly
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Ab initio molecular dynamics study of fluid H2O-CO2 mixture in broad pressure-temperature range2017In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 7, no 11, article id 115217Article in journal (Refereed)
    Abstract [en]

    Properties of H2O and CO2 fluid and their mixtures under extreme pressures and temperatures are poorly known yet critically important in a number of applications. Several hundreds of first-principles molecular dynamics (FPMD) runs have been performed to obtain the pressure-volume-temperature (P-V-T) data on supercritical H2O, CO2, and H2O-CO2 mixtures. The pressure-temperature (P-T) range are from 0.5 GPa to 104 GPa (48.5 GPa for CO2) and from 600 K to 4000 K. Based on these data, we evaluate several existing equations of state (EOS) for the fluid H2O, CO2, and H2O-CO2 mixture. The results show that the EOS for H2O from Belonoshko et al. [Geochim. Cosmochim. Acta 55, 381-387; Geochim. Cosmochim. Acta 55, 3191-3208; Geochim. Cosmochim. Acta 56, 3611-3626; Comput. Geosci. 18, 1267-1269] not only can be used in the studied P-T range but also is accurate enough to be used for prediction of P-V-T data. In addition, IAPWS-95 EOS for H2O shows excellent extrapolation behavior beyond 1.0 GPa and 1273 K. However, for the case of CO2, none of the existing EOS produces data in agreement with the FPMD results. We created new EOS for CO2. The precision of the new EOS is tested by comparison to the calculated P-V-T data, fugacity coefficient of the CO2 fluid derived from high P-T experimental data as well as to the (very scarce) experimental volumetric data in the high P-T range. On the basis of our FPMD data we created a new EOS for H2O-CO2 mixture. The new EOS for the mixture is in reasonable agreement with experimental data.

  • 14. Giblin, S. R.
    et al.
    Twengström, Mikael
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    et al.,
    Pauling entropy, metastability and equilibrium in Dy2Ti2O7spin iceManuscript (preprint) (Other academic)
  • 15.
    Hauschild, Johannes
    et al.
    Tech Univ Munich, Dept Phys, T42,James Franck Str 1, D-85748 Garching, Germany..
    Leviatan, Eyal
    Weizmann Inst Sci, Dept Condensed Matter Phys, IL-7610001 Rehovot, Israel..
    Bardarson, Jens H.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Altman, Ehud
    Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA..
    Zaletel, Michael P.
    Princeton Univ, Dept Phys, Princeton, NJ 08540 USA..
    Pollmann, Frank
    Tech Univ Munich, Dept Phys, T42,James Franck Str 1, D-85748 Garching, Germany..
    Finding purifications with minimal entanglement2018In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 98, no 23, article id 235163Article in journal (Refereed)
    Abstract [en]

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

  • 16.
    Hellsvik, Johan
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory. KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Thonig, Danny
    Modin, Klas
    Iusan, Diana
    Bergman, Anders
    Eriksson, Olle
    Bergqvist, Lars
    Delin, Anna
    General method for atomistic spin-lattice dynamics with first-principles accuracy2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 10, article id 104302Article in journal (Refereed)
    Abstract [en]

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

  • 17.
    Herviou, Loic
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Le Hur, Karyn
    Univ Paris Saclay, Ctr Phys Theor, CNRS, Ecole Polytech, F-91128 Palaiseau, France..
    Mora, Christophe
    Univ Paris Diderot, Univ Pierre & Marie Curie, Ecole Normale Super,PSL Res Univ, Lab Pierre Aigrain,Sorbonne Paris Cite,Sorbonne U, 24 Rue Lhomond, F-75231 Paris 05, France..
    Bipartite fluctuations and topology of Dirac and Weyl systems2019In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 7, article id 075133Article in journal (Refereed)
    Abstract [en]

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

  • 18.
    Javanmard, Younes
    et al.
    Max Planck Inst Phys Komplexer Syst, D-01187 Dresden, Germany..
    Trapin, Daniele
    Max Planck Inst Phys Komplexer Syst, D-01187 Dresden, Germany..
    Bera, Soumya
    Indian Inst Technol, Dept Phys, Bombay 400076, Maharashtra, India..
    Bardarson, Jens H.
    KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Heyl, Markus
    Max Planck Inst Phys Komplexer Syst, D-01187 Dresden, Germany..
    Sharp entanglement thresholds in the logarithmic negativity of disjoint blocks in the transverse-field Ising chain2018In: New Journal of Physics, ISSN 1367-2630, E-ISSN 1367-2630, Vol. 20, article id 083032Article in journal (Refereed)
    Abstract [en]

    Entanglement has developed into an essential concept for the characterization of phases and phase transitions in ground states of quantum many-body systems. In this work we use the logarithmic negativity to study the spatial entanglement structure in the transverse-field Ising chain both in the ground state and at nonzero temperatures. Specifically, we investigate the entanglement between two disjoint blocks as a function of their separation, which can be viewed as the entanglement analog of a spatial correlation function. We find sharp entanglement thresholds at a critical distance beyond which the logarithmic negativity vanishes exactly and thus the two blocks become unentangled, which holds even in the presence of long-ranged quantum correlations, i.e., at the system's quantum critical point. Using time-evolving block decimation, we explore this feature as a function of temperature and size of the two blocks and present a simple model to describe our numerical observations.

  • 19.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    (3+1)-Dimensional Schwinger Terms and Non-commutative Geometry1994In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 338, p. 241-248Article in journal (Refereed)
  • 20.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    A superversion of quasifree second quantization. I. Charged particles1992In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 3, no 3, p. 1032-1046Article in journal (Refereed)
  • 21.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Bc2(T) of anisotropic systems: some explicit results1990In: Physica B: Physics of Condensed Matter, Vol. 65, p. 1061-1062Article in journal (Refereed)
  • 22.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Cocycles for Boson and Fermion Bogoliubov Transformations1994In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 35, p. 96-112Article in journal (Refereed)
  • 23.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Consistent axial-like gauge fixing on hypertori1994In: Modern Physics Letters A, ISSN 0217-7323, E-ISSN 1793-6632, Vol. 9, p. 2913-2926Article in journal (Refereed)
  • 24.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Descent equations of Yang-Mills anomalies in noncommutative geometry1997In: Journal of Geometry and Physics, ISSN 0393-0440, E-ISSN 1879-1662, p. 259-279Article in journal (Refereed)
  • 25.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Elementary Derivation of the Chiral Anomaly1996In: Letters in Mathematical Physics, ISSN 0377-9017, E-ISSN 1573-0530, Vol. 6, p. 45-54Article in journal (Refereed)
  • 26.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Exactly solvable models for 2D correlated fermions2004In: Journal of Physics A: Mathematical and General, Vol. 37, no 2, p. 407-423Article in journal (Refereed)
    Abstract [en]

    I discuss many-body models for correlated fermions in two space dimensions which can be solved exactly using group theory. The simplest example is a model of a quantum Hall system: two-dimensional (2D) fermions in a constant magnetic field and a particular non-local four-point interaction. It is exactly solvable due to a dynamical symmetry corresponding to the Lie algebra gl∞ ⊕ gl∞. There is an algorithm to construct all energy eigenvalues and eigenfunctions of this model. The latter are, in general, many-body states with spatial correlations. The model also has a non-trivial zero temperature phase diagram. I point out that this QH model can be obtained from a more realistic one using a truncation procedure generalizing a similar one leading to mean field theory. Applying this truncation procedure to other 2D fermion models I obtain various simplified models of increasing complexity which generalize mean field theory by taking into account non-trivial correlations but nevertheless are treatable by exact methods.

  • 27.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Fermion Current Algebras and Schwinger Terms in 3+1 Dimensions1994In: Communications in Mathematical Physics, ISSN 0010-3616, E-ISSN 1432-0916, Vol. 162, p. 1-32Article in journal (Refereed)
  • 28.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Fermi-surface harmonics in the theory of the upper critical field1992In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 46, no 14, p. 9104-Article in journal (Refereed)
  • 29.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Finding and solving Calogero-Moser type systems using Yang-Mills gauge theories1999In: Nuclear Physics B, ISSN 0550-3213, E-ISSN 1873-1562, Vol. 563, p. 506-532Article in journal (Refereed)
  • 30.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Gauge Theories on a Cylinder1992In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 296, p. 117-120Article in journal (Refereed)
  • 31.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Gribov ambiguity and non-trivial vacuum structure of gauge theories on a cylinder1993In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 303, p. 303-307Article in journal (Refereed)
  • 32.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Loop groups, anyons and the Calogero-Sutherland model1999In: Communications in Mathematical Physics, ISSN 0010-3616, E-ISSN 1432-0916, Vol. 201, p. 1-34Article in journal (Refereed)
  • 33.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Mean field approach to antiferromagnetic domains in the doped Hubbard model1997In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, p. 9439-9451Article in journal (Refereed)
  • 34.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Non-commutative Integration Calculus1995In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 36, p. 3822-3835Article in journal (Refereed)
  • 35.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Novel integrable spin-particle models from gauge theories on a cylinder1998In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 429, p. 336-342Article in journal (Refereed)
  • 36.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    On current superalgebras and super-Schwinger terms1991In: Letters in Mathematical Physics, ISSN 0377-9017, E-ISSN 1573-0530, no 1, p. 69-76Article in journal (Refereed)
  • 37.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    On the upper critical field of anisotropic superconductors1991In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 73, p. 347-356Article in journal (Refereed)
  • 38.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Orthogonality of super‐Jack polynomials and a Hilbert space interpretation of deformed Calogero–Moser–Sutherland operators2019In: Bulletin of the London Mathematical Society, ISSN 0024-6093, E-ISSN 1469-2120, Vol. 51, no 2, p. 353-370Article in journal (Refereed)
  • 39.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    QCD(1+1) with massless quarks and gauge covariant Sugawara construction1994In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 341, p. 195-204Article in journal (Refereed)
  • 40.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Quantum Gauge Theories and Noncommutative Geometry1996In: Acta Physica Polonica B, ISSN 0587-4254, E-ISSN 1509-5770, Vol. 27, p. 2477-2496Article in journal (Refereed)
  • 41.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Scattering matrix in external field problems1996In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 37, p. 3933-3953Article in journal (Refereed)
  • 42.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Strong coupling gauge theory, quantum spin systems and the spontaneous breaking of chiral symmetry1992In: Physics Letters B, ISSN 0370-2693, E-ISSN 1873-2445, Vol. 297, p. 175-180Article in journal (Refereed)
  • 43.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    SU (N) antiferromagnets and strongly coupled QED: effective field theory for Josephson junctions arrays1993In: Nuclear physics B, Proceedings supplements, ISSN 0920-5632, E-ISSN 1873-3832, Vol. 33, p. 192-208Article in journal (Refereed)
  • 44.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Supersymmetry breaking and the Jaynes-Cummings model1993In: Physics Letters A, ISSN 0375-9601, E-ISSN 1873-2429, Vol. 176, no 5, p. 307-312Article in journal (Refereed)
  • 45.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    The BCS critical temperature in a weak homogeneous magnetic field2019In: Journal of Spectral Theory, ISSN 1664-039X, E-ISSN 1664-0403Article in journal (Refereed)
  • 46.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    The critical temperature of superconductors with a cylinder symmetrical Fermi surface1989In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 157, no 3, p. 415-424Article in journal (Refereed)
  • 47.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    The geometric phase and the Schwinger term in some models1992In: International Journal of Modern Physics A, ISSN 0217-751X, E-ISSN 1793-656X, Vol. 7, no 21, p. 5045-5083Article in journal (Refereed)
  • 48.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    The Luttinger-Schwinger Model1997In: Annals of Physics, ISSN 0003-4916, E-ISSN 1096-035X, Vol. 253, p. 310-331Article in journal (Refereed)
  • 49.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    The Superfluidity and Experimental Properties of Odd-Energy-Gap Superconductors1993In: Europhysics letters, ISSN 0295-5075, E-ISSN 1286-4854, Vol. 26, no 2Article in journal (Refereed)
  • 50.
    Langmann, Edwin
    KTH, School of Engineering Sciences (SCI), Physics, Mathematical Physics. KTH, School of Engineering Sciences (SCI), Physics, Condensed Matter Theory.
    Theory of the upper critical magnetic field without local approximation1989In: Physica. C, Superconductivity, ISSN 0921-4534, E-ISSN 1873-2143, Vol. 59, p. 561-569Article in journal (Refereed)
12 1 - 50 of 59
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