Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Y29: Higher Spin Kitaev Honeycomb MagnetsInvited Live Streamed
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Sponsoring Units: GMAG DCMP Chair: Harald Jeschke, Okayama University Room: McCormick Place W-190B |
Friday, March 18, 2022 8:00AM - 8:36AM |
Y29.00001: Quantum spin liquid in the semiclassical regime Invited Speaker: Ioannis Rousochatzakis Quantum spin liquids (QSLs) have been at the forefront of correlated electron research ever since their proposal in 1973, and the realization that they belong to the broader class of intrinsic topological orders. According to received wisdom, QSLs can arise in frustrated magnets with low spin S, where strong quantum fluctuations act to destabilize conventional, magnetically ordered states. Here, we present a Z2 QSL ground state that appears already in the semiclassical, large-S limit. This state has both topological and symmetry-related ground-state degeneracy, and two types of gaps, a "magnetic flux" gap that scales linearly with S and an "electric charge" gap that drops exponentially in S. The magnet is the spin-S version of the spin-1/2 Kitaev honeycomb model, which has been the subject of intense studies in correlated electron systems with strong spin–orbit coupling, and in optical lattice realizations with ultracold atoms. |
Friday, March 18, 2022 8:36AM - 9:12AM |
Y29.00002: Low-energy and thermodynamic properties of spin-S Kitaev models Invited Speaker: Joji Nasu The Kitaev model is an S=1/2 quantum spin model with bond-dependent interactions on a honeycomb lattice and possesses gapless and gapped quantum spin liquids. There are two types of elementary excitations in this model: itinerant Majorana fermions and localized Z2 fluxes. Moreover, in the case where one of three types of bonds is stronger than the others, the Z2 fluxes dominate the low-energy physics described by the toric code. While the low-energy properties of the S=1/2 Kitaev model have been studied intensively, features in the extension to higher magnitudes of S remain elusive. In this study, we investigate the finite-temperature properties and anisotropic limit of spin-S Kitaev models. At finite temperatures, the specific heat exhibits the double-peak structure in the S=1/2 Kitaev model due to fractionalization into Majorana and Z2 quasiparticles. We find that this structure also appears in the higher-S Kiteav models, and the entropy is well scaled by S, which are obtained by calculations using thermal pure quantum states. To clarify the difference by the magnitude of S, we focus on the anisotropic limit of the higher-S Kiteav models. We find that the effective Hamiltonian depends on whether S is integer or half-integer, similar to the Haldane conjecture. The anisotropic Kitaev model is mapped onto the toric code with topological order for the half-integer spin systems but onto a topologically-trivial model for integer spin systems. The result indicates that quantum fluctuations play a crucial role in the ground state, particularly in half-integer systems. |
Friday, March 18, 2022 9:12AM - 9:48AM |
Y29.00003: Unveiling the S=3/2 Kitaev Honeycomb Spin Liquids Invited Speaker: Hui-Ke Jin The S=3/2 Kitaev honeycomb model (KHM) has defied an analytical as well as numerical understanding because it is not exactly soluble like its S=1/2 brethren and in contrast to other spin-S Kitaev models numerical methods are plagued by a massive pile up of low energy states. Here, we uncover the phase diagram of the S=3/2 KHM and find gapped and gapless quantum spin liquids (QSLs) generally coexisting with spin quadrupolar orders. Employing an SO(6) Majorana fermion representation of spin-3/2's, we find an exact representation of the conserved plaquette fluxes in terms of static Z 2 gauge fields akin to the S=1/2 KHM which enables us to treat the remaining interacting matter fermion sector in a parton mean-field theory. The latter provides an explanation for the extensive near degeneracy of low energy states in the gapless phase via the appearance of almost flat Majorana bands close to zero energy. Our parton description is in remarkable quantitative agreement with numerical simulations using the density matrix renormalization group method, and is furthermore corroborated by the addition of a single ion anisotropy which continuously connects the gapless Dirac QSL of our model with that of the S=1/2 KHM. We discuss the implications of our findings for materials realization of higher S=3/2 KHMs and the stability of the QSL phase with respect to additional interactions. |
Friday, March 18, 2022 9:48AM - 10:24AM |
Y29.00004: Antisymmetric versus anisotropic exchange: shaping topological excitation spectra and transport properties of Heisenberg-Kitaev magnets Invited Speaker: Fabian R Lux Ever since their conception, Kitaev interactions have been a continuous source of exotic topological topological effects in the field of quantum magnetism. This concerns not only the ground state properties of Kitaev materials which potentially host Majorana fermions, but also their magnonic excitation spectra. In honeycomb Heisenberg-Kitaev magnets, the anisotropic bond-directional exchange interactions can lead to the emergence of a topological magnon-insulator, characterized by a nontrivial first Chern number. The magnon spectrum bears witness to the underlying magnetic interactions, and can in principle be used to quantify the relevance of anisotropic exchange experimentally by the means of ineleastic neutron scattering. Spin-orbit coupling, which is the major driving force behind those interactions, can however lead to other magnetic interactions such as the Dzyaloshinskii-Moriya interaction (DMI) which might interfere in this procedure [1]. By referring to linear spin wave theory, we study the honeycomb Heisenberg-Kitaev model in the presence of DMI in order to understand the competition between the spin-orbit driven DMI and Kitaev interaction and its impact on the magnon spectrum and thermal transport properties [2]. Based on our results, we propose a strategy to disentangle the two types of interactions experimentally and explore magnon-induced electronic orbital magnetism as a new channel which can reveal the complexity of magnetic interactions [3]. |
Friday, March 18, 2022 10:24AM - 11:00AM |
Y29.00005: New Types of Kitaev Magnets with 3d Metal and Heavy Ligands Invited Speaker: Changsong Xu Most of recent studies on quantum spin liquids (QSL) has been devoted to the Kitaev model, which is exactly solvable for S=1/2 and where the Kitaev interaction is bond-dependent anisotropic exchange coupling, thus requiring strong spin-orbit coupling (SOC). Such rigorous requirements lead to very limited candidates, i.e., RuCl3 and Na2IrO3, for which the Kitaev interaction results from edge-sharing octahedra and 4d/5d transition metal with strong SOC. In this talk, I will review on recent developments of Kitaev platforms from 4d/5d transition metal compounds to a large series of 3d systems, where the necessary strong SOC are provided by the bridging heavy ligands. Three types of systems, (i) CrI3 and CrSiTe3 type, (ii) NiI2 type and (iii) Na3Co2SbO6 type, each with different spin value, will be introduced. I will mainly focus on their different magnetic interactions from first-principles, but also talk about the attempts to discover possible QSL there. |
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