Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session W56: Quantum Spin Liquids, Theory II |
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Sponsoring Units: GMAG Chair: Martin Mourigal, Georgia Tech Room: Room 304 |
Thursday, March 9, 2023 3:00PM - 3:12PM |
W56.00001: Planar thermal Hall effect from phonons in a Kitaev candidate material Lu Chen, Etienne Lefrancois, Ashvini Vallipuram, Quentin Barthélemy, Amirreza Ataei, Weiliang Yao, Yuan Li, Louis Taillefer Kitaev materials are a promising platform for the realization of quantum spin liquid states. The thermal Hall effect has emerged as a potential probe of exotic excitations within such states. In the Kitaev material α-RuCl3, however, the thermal Hall conductivity κxy has been attributed not only to exotic Majorana fermions [1,2] or chiral magnons [3], but also to phonons [4]. It has been shown theoretically that the former two types of heat carriers can generate a “planar” thermal Hall effect [5-7], whereby the magnetic field is parallel to the heat current, as observed experimentally [3,8], but it is unknown whether phonons also could. Here we show that a planar thermal Hall effect is present in another Kitaev material, Na2Co2TeO6. On the basis of a striking similarity between the temperature and field dependence of κxy and that of the phonon-dominated thermal conductivity κxx, we argue that the planar thermal Hall effect in Na2Co2TeO6 is generated by phonons. |
Thursday, March 9, 2023 3:12PM - 3:24PM |
W56.00002: Characterizing emergent spin liquids in the extended Kitaev honeycomb model: a hierarchical mean-field approach William Holdhusen, Daniel Huerga, Gerardo Ortiz The Kitaev honeycomb model represents a paradigmatic example of a topologically-ordered quantum spin liquid (the Kitaev spin liquid, or KSL). Due to its exactly-solvable nature, a great deal is known about the properties of its ground state phases. Recent theoretical work has demonstrated a rich array of states generated by adding additional terms to the Kitaev model, even in the case of a simple applied magnetic field. We study the Kitaev model in external magnetic field with hierarchical mean-field theory (HMFT), a method based on the use of clusters as the basic degrees of freedom that allows to uncover phase diagrams of frustrated quantum magnetism in the thermodynamic limit. Benchmark numerical results with clusters of up to 24 spins and finite size scaling show that HMFT accurately describes the exact phase diagram at zero field, allowing us to identify the gapless Kitaev spin liquid as a chiral magnet whose long range order vanishes upon increasing the cluster size. Upon adding a [111] external magnetic field, we find a phase diagram hosting various phases characterized by chirality and nonzero topological entanglement entropy, in qualitative agreement with other methods, as well as an intermediate partially polarized phase with topological order that has not been previously identified. |
Thursday, March 9, 2023 3:24PM - 3:36PM |
W56.00003: Kitaev exchange in new Ruthenium-based honeycomb and triangular lattice compounds David Kaib, Aleksandar Razpopov, Kira Riedl, Francesco Ferrari, Ying Li, Steffen Backes, Igor I Mazin, Roser Valenti In the hunt for the realization of the celebrated Kitaev spin liquid, the (arguably) closest realization so far has been α-RuCl3, which nevertheless orders with zigzag antiferromagnetic order. |
Thursday, March 9, 2023 3:36PM - 3:48PM |
W56.00004: Magnetic field induced topological transitions and thermal conductivity in a generalized Kitaev model Heqiu Li, Yong-Baek Kim, Hae-Young Kee Recent experiments on Kitaev spin liquid candidate materials reported nonmonotonic behavior of thermal conductivity as a function of magnetic field, which lead to conflicting interpretations of its origin. Motivated by this development, we study the magnetic field dependence of thermal conductivity of a generalized Kitaev model, which allows the phase transitions between different flux sectors as a function of the magnetic field. The thermal conductivity due to Majorana fermions shows dip-bump structures as the magnetic field increases, which is caused by either the transitions between different flux sectors of Kitaev spin liquids or the topological transitions that change the Majorana Chern number within the same flux sector. It is shown that the change in Chern number is closely related to the four-Majorana-fermion interaction induced by the magnetic field. The nonmonotonic behavior in thermal conductivity emerges at finite temperature, and it becomes weaker when temperature decreases toward zero. Our model provides a generic mechanism for the Kitaev spin liquids to develop nonmonotonic magnetic-field dependence of thermal conductivity while the comparison to realistic materials remains an open question for future investigation. |
Thursday, March 9, 2023 3:48PM - 4:00PM |
W56.00005: Nesting instability of gapless U(1) spin liquids with spinon Fermi pockets in two dimensions Wilhelm G Krüger, Lukas Janssen Quantum spin liquids are exotic states of matter that may be realized in frustrated quantum magnets and feature fractionalized excitations and emergent gauge fields. Here, we consider a gapless U(1) spin liquid with spinon Fermi pockets in two spatial dimensions. Such a state appears to be the most promising candidate to describe the exotic field-induced behavior observed in numerical simulations of the antiferromagnetic Kitaev honeycomb model. A similar such state may also be responsible for the recently-reported quantum oscillations of the thermal conductivity in the field-induced quantum paramagnetic phase of α-RuCl3. We consider the regime close to a Lifshitz transition, at which the spinon Fermi pockets shrink to small circles around high-symmetry points in the Brillouin zone. By employing renormalization group and mean-field arguments, we demonstrate that interactions lead to a gap opening in the spinon spectrum at low temperatures, which can be understood as a nesting instability of the spinon Fermi surface. This leads to proliferation of monopole operators of the emergent U(1) gauge field and confinement of spinons. While signatures of fractionalization may be observable at finite temperatures, the gapless U(1) spin liquid state with nested spinon Fermi pockets is ultimately unstable at low temperatures towards a conventional long-range-ordered ground state, such as a valence bond solid. Implications for Kitaev materials in external magnetic fields are discussed. |
Thursday, March 9, 2023 4:00PM - 4:12PM |
W56.00006: The Electric Field Effects on Kitaev Quantum Spin Liquids Pureum Noh, Kyusung Hwang, Eun-Gook Moon The ground state of Kitaev's honeycomb model is a non-abelian chiral spin-liquid state with Majorana fermion excitations, which has been proposed as a promising platform for fault-tolerant topological quantum computations. Here, we show that Majorana fermions can be manipulated by applying an electric field. By using a combination of exact diagonalization and parton analysis for microscopic spin Hamiltonians, it is demonstrated that the manipulation is most significant near topological phase transitions of Kitaev's quantum spin liquids. We also discuss experimental signatures to detect Kitaev quantum spin liquids in experiments, especially in connection with the candidate materials such as $alpha$-RuCl$_3$. |
Thursday, March 9, 2023 4:12PM - 4:24PM |
W56.00007: Emergent symmetry and fractionalized Goldstone modes in a bilayer quantum spin liquid Aayush Vijayvargia, Emilian M Nica, Yuan-Ming Lu, Onur Erten I will present the phase diagram of a bilayer quantum spin liquid model with Kitaev-like interactions |
Thursday, March 9, 2023 4:24PM - 4:36PM |
W56.00008: Dynamics of Visons and Thermal Hall effect in Perturbed Kitaev models Aprem Joy, Achim Rosch A vison is an excitation of the Kitaev spin liquid which carries a Z2 gauge flux. While immobile in the pure Kitaev model, it becomes a dynamical degree of freedom in the presence of perturbations. We study an isolated vison in the isotropic Kitaev model perturbed by a small external magnetic field h, an off-diagonal exchange interaction Γ, and a Heisenberg coupling J. In the ferromagnetic Kitaev model, the dressed vison obtains a dispersion linear in Γ and h and a fully universal low-T mobility, μ=6?v2m/(kBT)2, where vm is the velocity of Majorana fermions. In contrast, in the antiferromagnetic (AFM) Kitaev model interference effects suppress coherent propagation and an incoherent Majorana-assisted hopping leads to a T-independent mobility. The motion of a single vison due to Heisenberg interactions is strongly suppressed for both signs of the Kitaev coupling. Vison bands in AFM Kitaev models can be topological and may lead to characteristic features in the thermal Hall effects in Kitaev materials. Furthermore, we argue that vison diffusion leads to universal signatures in quench experiments. |
Thursday, March 9, 2023 4:36PM - 4:48PM |
W56.00009: Thermal Hall conductivity near field-suppressed magnetic order in a Kitaev-Heisenberg model Aman Kumar We investigate thermal Hall conductivity κxy of a J-K Kitaev-Heisenberg model with a Zeeman field in the (111) direction in the light of the recent debate surrounding the possible re-emergence of Ising topological order (ITO) and half-quantized κxy/T upon field-suppression of long-range magnetic order in Kitaev materials. We use the purification-based finite temperature Tensor Network approach making no prior assumptions about the nature of the excitations: Majorana, visons or spin waves. For purely Kitaev interactions and fields h/K>0.02 sufficient to degrade ITO, the peak κxy/T monotonously decreases from half-quantization associated with lower fields - a behavior reminiscent of vison fluctuation corrections. In our J-K model (with ferro-K and antiferro-J), in the vicinity of field-suppressed magnetic order, we found κxy/T to be significant, with peak magnitudes exceeding half-quantization followed by a monotonous decrease with increasing h. We thus conclude that half-quantized thermal Hall effect, if found in our model in the vicinity of field suppressed magnetic order, is a fine-tuning effect and is not associated with a Majorana Hall state with ITO. |
Thursday, March 9, 2023 4:48PM - 5:00PM |
W56.00010: Classification of classical spin liquid Han Yan, Owen M Benton, Andriy H Nevidomskyy, Roderich Moessner Classical spin liquids (CSL) are arguably one of the most interesting types of classical matter, offering a canvas from which emergent quantum phases can emerge. Described by the classical limit of gauge theories (electrostatics), these CSL can be upgraded to topological orders or gapless quantum liquid states if equipped with proper quantum dynamics. |
Thursday, March 9, 2023 5:00PM - 5:12PM |
W56.00011: Frequency-resolved functional renormalization group for quantum magnetic systems Janik Potten, Tobias Mueller, Ronny Thomale Strongly correlated materials are one of the most prolific topics of contemporary condensed matter physics. Within this field, the functional renormalization group (FRG) approach for spin models relying on a pseudo-fermionic description has proven to be a very powerful technique in simulating ground state properties of strongly frustrated magnetic lattices. However, the FRG as well as many other theoretical models, suffer from the fact that they are formulated in the imaginary-time Matsubara formalism and thus are only able to predict static correlations directly. Nevertheless, describing the dynamical properties, especially of magnetic systems is one of the fundamental theoretical challenges, as they are the key to bridging the gap to experimental data from neutron scattering experiments. |
Thursday, March 9, 2023 5:12PM - 5:24PM |
W56.00012: Quantum correlation, entanglement and influnece of magnon Hall effect on some quantum spin systems LEONARDO S LIMA Quantum correlations and entanglement in some quantum spin systems as the nearest-neighbor Heisenberg model on Lieb lattice (LL) with out-of-plane Dzyaloshinskii-Moriya (DMI) antissimetric spins coupling and external magnetic field was studied [1,2]. We obtain the behaviour of the von Neumann entropy (VN) and entanglement negativity as a function of the DMI interaction, analyzing the effect of magnon bands on quantum entanglement. Furthermore, quantum correlations in some fermions models such as the two-dimensional non-Hermitian model (NH) on LL lattice and the tight-binding model (TB) on the LL lattice have been also investigated. In these models, we analyze the effect of opening of the gap in the spectrum in quantum entanglement quantifiers as von Neumann entropy and entanglement negativity. In addition, we analyze quantum correlations in other models as well: in the two-dimensional Heisenberg model on checkerboard and honeycomb lattices[3,4] as well as in other non-Hermitian quantum spin systems [5]. |
Thursday, March 9, 2023 5:24PM - 5:36PM |
W56.00013: Non-Linear Dynamics of Frustrated Magnets Ciaran Hickey Magnetic frustration can, in some cases, be strong enough so as to completely suppress long-range magnetic order. In the classical limit, this results in so-called "classical spin liquids". Such spin liquids possess a highly unconventional excitation spectrum, often consisting, within the context of linear response, of a broad and relatively featureless continuum across both energy and momentum. Here, I will discuss how non-linear response, as probed via two-dimensional coherent spectroscopy, can be used to reveal sharp features of classical spin liquids, and compare and contrast these features with those of conventional long-range ordered phases. |
Thursday, March 9, 2023 5:36PM - 5:48PM |
W56.00014: Analytic Approach to Calculating Vison Gaps in Kitaev spin liquids and odd-frequency superconductors Aaditya Panigrahi, Piers Coleman, Alexei Tsvelik We present an analytic approach to calculating the vison gap in Kitaev and Yao Lee spin liquids, in which the energy for flipping a $Z_2$ bond can be computed in terms of a scattering phase shift. Our result reproduces the known numerical result E = 0.2672 J for the Kitaev spin liquid[1,2], and is readily generalized to infinitely separated visons, allowing us to demonstrate the development of a topological state in the toric code. Using this method, we examine the vison energy in the CPT model[2], where a Kondo coupling to a 3D Yao-Lee spin liquid drives a spontaneous pairing instability into an odd-frequency triplet superconductor S=1/2 spinor order. The vison energy remains finite even at strong coupling, where fractionalized superconductivity is replaced by a conventional Kondo insulator embedded in a gapless orbital spin liquid. |
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