6,040 research outputs found

    Thermal Hall effects due to topological spin fluctuations in YMnO_3

    Get PDF
    The thermal Hall effect in magnetic insulators has been considered a powerful method for examining the topological nature of charge-neutral quasiparticles such as magnons. Yet, unlike the kagome system, the triangular lattice has received less attention for studying the thermal Hall effect because the scalar spin chirality cancels out between adjacent triangles. However, such cancellation cannot be perfect if the triangular lattice is distorted. Here, we report that the trimerized triangular lattice of multiferroic hexagonal manganite YMnO3 produces a highly unusual thermal Hall effect under an applied magnetic field. Our theoretical calculations demonstrate that the thermal Hall conductivity is related to the splitting of the otherwise degenerate two chiralities of its 120Ëš magnetic structure. Our result is one of the most unusual cases of topological physics due to this broken Z2 symmetry of the chirality in the supposedly paramagnetic state of YMnO3, due to strong topological spin fluctuations with the additional intricacy of a Dzyaloshinskii-Moriya interaction

    Optical Spectroscopy of 3d and 4d correlated electron systems.

    Get PDF
    In the context of this work, three different materials are studied via optical spec- troscopy methods. The three materials are La2Cu2O5, Fe3O4, and Ca2RuO4, where the first one is investigated via Fourier spectroscopy, while the latter two are stud- ied via spectroscopic ellipsometry

    Renormalization of antiferromagnetic magnons by superconducting condensate and quasiparticles

    Full text link
    The ability to modify and tune the spin-wave dispersion is one of the most important requirements for engineering of magnonic networks. In this study we demonstrate the promise of synthetic thin-film hybrids composed of an antiferromagnetic insulator (AF) and a normal (N) or superconducting (S) metal for tuning and modifying the spin-wave dispersion in antiferromagnetic insulators. The key ingredient is the uncompensated magnetic moment at the AF/S(N) interface, which induces an effective exchange field in the adjacent metal via the interface exchange interaction. The exchange field spin polarizes quasiparticles in the metal and induces spinful triplet Cooper pairs screening the magnon. The quasiparticle and Cooper pair polarization renormalizes the magnon dispersion. The renormalization results in the splitting of the otherwise degenerate AF magnon modes with no need to apply a magnetic field. It is also proposed that measurements of the renormalized dispersion relations can provide the amplitude of the effective exchange field induced by the AF in the adjacent metal

    Quantum light-matter interactions in structured waveguides

    Full text link
    We explore special features of quantum light-matter interactions inside structured waveguides due to their finite bandwidth, band edges, and non-trivial topological properties. We model the waveguides as either a tight-binding (TB) chain or a Su-Schrieffer-Heeger (SSH) chain. For unstructured waveguides with infinite bandwidth, the transmission and reflection amplitude of a side-coupled two-level emitter (2LE) are the same as the reflection and transmission amplitude of a direct-coupled 2LE. We show that this analogy breaks down for structured waveguides with finite bandwidth due to the appearance of Lamb shift only for the direct-coupled 2LE. We further predict a robust light-emitter coupling at zero collective decay width of a single giant 2LE (with two couplings at different points) near the band edges of the structured waveguides where topological features can be beneficial. Finally, we study single-photon dynamics in a heterojunction of a long TB and short SSH waveguide connected to a 2LE at the SSH end. We show the propagation of a photon from the excited emitter to the TB waveguide only when the SSH waveguide is in the topological phase. Thus, the heterojunction acts as a quantum switch or conditional propagation channel.Comment: 15 pages, 11 figure

    Signatures of many-body localization of quasiparticles in a flat band superconductor

    Full text link
    We construct a class of exact eigenstates of the Hamiltonian obtained by projecting the Hubbard interaction term onto the flat band subspace of a generic lattice model. These exact eigenstates are many body states in which an arbitrary number of localized fermionic particles coexist with a sea of mobile Cooper pairs with zero momentum. By considering the dice lattice as an example, we provide evidence that these exact eigenstates are in fact manifestation of local integrals of motions of the projected Hamiltonian. In particular the spin and particle densities retain memory of the initial state for a very long time, if localized unpaired particles are present at the beginning of the time evolution. This shows that many-body localization of quasiparticles and superfluidity can coexist even in generic two-dimensional lattice models with flat bands, for which it is not known how to construct local conserved quantities. Our results open new perspectives on the old condensed matter problem of the interplay between superconductivity and localization.Comment: 20 Pages, 9 figure

    Mirror-protected Majorana zero modes in ff-wave multilayer graphene superconductors

    Full text link
    Inspired by recent experimental discoveries of superconductivity in chirally-stacked and twisted multilayer graphene, we study models of ff-wave superconductivity on the honeycomb lattice with arbitrary numbers of layers. These models respect a mirror symmetry that allows classification of the bands by a mirror-projected winding number ν±\nu_\pm. For odd numbers of layers, the systems are topologically nontrivial with ν±=±1\nu_\pm = \pm 1. Along each mirror-preserving edge in armchair nanoribbons, there are two protected Majorana zero modes. These modes are present even if the sample is finite in both directions, such as in rectangular and hexagonal flakes. Crucially, zero modes can also be confined to vortex cores, which can be created by a magnetic field or localized magnetic impurities and accessed by local scanning probes. Finally, we apply these models to twisted bilayer and trilayer systems, which also feature boundary-projected and vortex-confined zero modes. Since vortices are experimentally accessible, our study suggests that superconducting multilayer graphene systems are promising platforms to create and manipulate Majorana zero modes.Comment: Comments are greatly appreciated. 8 + 22 pages with 4 + 15 figure

    Boundary integral representation of multipliers of fragmented affine functions and other intermediate function spaces

    Full text link
    We develop a theory of abstract intermediate function spaces on a compact convex set XX and study the behaviour of multipliers and centers of these spaces. In particular, we provide some criteria for coincidence of the center with the space of multipliers and a general theorem on boundary integral representation of multipliers. We apply the general theory in several concrete cases, among others to strongly affine Baire functions, to the space Af(X)A_f(X) of fragmented affine functions, to the space (Af(X))μ(A_f(X))^\mu, the monotone sequential closure of Af(X)A_f(X), to their natural subspaces formed by Borel functions, or, in some special cases, to the space of all strongly affine functions. In addition, we prove that the space (Af(X))μ(A_f(X))^\mu is determined by extreme points and provide a large number of illustrating examples and counterexamples.Comment: 136 pages; we corrected one definition and expanded the introduction a bi

    Emergent criticality in fully frustrated quantum magnets

    Full text link
    Phase transitions in condensed matter are often linked to exotic emergent properties. We study the fully frustrated bilayer Heisenberg antiferromagnet to demonstrate that an applied magnetic field creates a novel emergent criticality. The quantum phase diagram contains four states, the DS (singlets on every interlayer dimer bond), DTAF (all triplets with antiferromagnetic order), TC (a singlet-triplet checkerboard) and FM (saturated ferromagnet). The thermal phase diagram is dominated by a wall of discontinuities extending from the zero-field DTAF-DS transition to a quantum critical endpoint where the field drives the DTAF and TC into the FM. This first-order wall is terminated at finite temperatures by a line of critical points, where the Berezinskii-Kosterlitz-Thouless (BKT) transition of the DTAF and the thermal Ising transition of the TC also terminate. We demonstrate by quantum Monte Carlo simulations that the BKT transition does not change the Ising nature of the DTAF-DS critical line. By contrast, the combination of symmetries merging on the multicritical DTAF-TC line leads to a 4-state Potts universality not contained in the microscopic Hamiltonian, which we associate with the Ashkin-Teller model. Our results represent a systematic step in understanding emergent phenomena in quantum magnetic materials including the ``Shastry-Sutherland compound'' SrCu2_2(BO3_3)2_2.Comment: 10+8 pages, 5+7 figure

    The Study of Excitons in 2D Novel Materials and Their van der Waals Heterostructures in the Magnetic Field

    Full text link
    This research focuses on the direct and indirect excitons in Rydberg states in monolayers, bilayers, and van der Waals heterostructures composed of 2D semiconductors in the presence of the external magnetic field. In our work, we report binding energies of direct and indirect excitons in Rydberg states, the energy contribution from the magnetic field to the binding energies of magnetoexcitons, and diamagnetic coefficients (DMCs) of magnetoexcitons. We study isotropic materials: transition metal dichalcogenides, TMDCs (WSe2, WS2, MoSe2, MoS2), and Xenes (silicene, germanene, stanene), and anisotropic materials: phosphorene and transition metal trichalcogenides, TMTCs (TiSe3, TiS3, ZrSe3, ZrS3). For excitons in TMDCs, phosphorene, and TMTCs, we consider freestanding (FS) and encapsulated by hexagonal boron nitride (hBN) monolayers, FS bilayers, and van der Waals heterostructures (vdWHs) when the external magnetic field is perpendicular to the structure. In vdWHs, the top and bottom 2D semiconductor monolayers are separated by the number of hBN layers, N. For excitons in Xenes, we consider FS and hBN-encapsulated monolayers and vdWHs when the external electric and magnetic fields are perpendicular to the structure. Excitons in TMDCs and Xenes structures are studied when the external magnetic field is varied between 0 and 30 T, and for Xenes, the electric field is taken above the critical value which is unique for each material up to the value where a Xene monolayer becomes unstable. Excitons in TMTCs and phosphorene structures are studied when the magnetic field is varied between 0 and 60 T. In our approach, within the framework of the effective mass approximation, we solve the Schrodinger equation for an interacting electron and hole. For direct excitons in a monolayer, we use the Rytova-Keldysh (RK) potential to describe interactions between an electron and hole. For indirect excitons in a bilayer and vdWH, we use the Rytova-Keldysh and Coulomb potentials to describe interactions between an electron and hole located in two different monolayers. This allows us to investigate the role of the screening in TMDCs, Xenes, TMTCs, and phosphorene. We show that the energy contribution from the magnetic field to the binding energies and DMCs of direct and indirect magnetoexcitons can be tuned by the magnetic field. For magnetoexcitons in Xenes, the electric field is an additional degree of freedom that can be used to tune binding energies, energy contribution from the magnetic field to the binding energies, and DMCs. Moreover, in vdWHs, we show that varying the number of hBN layers is an additional degree of freedom that can be used to tailor binding energies, energy contribution from the magnetic field to the binding energies, and DMCs. The results reported in this work on excitons in TMDCs vdWHs and in TMTCs, Xenes, and phosphorene structures are the first of their kind. They can be compared with the experimental results when they become available
    • …
    corecore