Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session A67: Thermal Hall Effect in Quantum MaterialsInvited
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Sponsoring Units: DCMP Chair: Leon Balents, University of California, Santa Barbara Room: Four Seasons 2-3 |
Monday, March 2, 2020 8:00AM - 8:36AM |
A67.00001: Thermal Hall conductivity of spin liquids at low temperatures Invited Speaker: N. Phuan Ong I will describe results on low-temperature thermal Hall conductivity Kxy of several quantum spin liquids based on honeycomb and triangular lattices, primarilty α-RuCl3, and Na2BaCo(PO4)2. In α-RuCl3, I will describe recent evidence suggesting the existence of a neutral Fermi surface. Results on the thermal Hall conductivity at temperatures performed at temperatures down to 0.4 K will be presented. The difficult challenges facing Kxy measurements will be discussed. |
Monday, March 2, 2020 8:36AM - 9:12AM |
A67.00002: Thermal Hall effect of α-RuCl3 Invited Speaker: Christian Hess For several years, the compound α-RuCl3 is considered as one prime candidate material to host a Kitaev topological quantum spin liquid (TQSL). Such a TQSL has been predicted for the spin-1/2 Kitaev model on a honeycomb lattice in an external magnetic field [1]. The zero field ground state is a quantum spin liquid with itinerant Majorana fermions and immobile gauge fluxes as elementary excitations. An external magnetic field gaps out the Majorana bulk states and topological Majorana edge states emerge. Indeed, for α-RuCl3 there is evidence for a significant Kitaev interaction acting between neighboring jeff=1/2 moments. However, the ground state of α-RuCl3 shows long-range antiferromagnetic order, indicative of additional Heisenberg-type and anistropy terms in the spin Hamiltonian. An in-plane field of about 8 T suppresses the magnetic order, which opens the question whether the field-induced ground state bears the main signatures of the Kitaev TQSL. In this talk, I will discuss our experimental efforts to probe the elementary magnetic excitations of α-RuCl3 by thermal transport. After summarizing the main findings for the longitudinal heat conductivity κxx [2], and briefly discussing new data which extend our findings to very large magnetic fields and lower temperature, I will focus on the surprising and sizeable thermal Hall effect κxy with a field perpendicular to the RuCl3-planes [3] as well as on our attemps to study this quantity for different field orientations. |
Monday, March 2, 2020 9:12AM - 9:48AM |
A67.00003: Giant thermal Hall conductivity in the pseudogap phase of cuprate superconductors Invited Speaker: Gael Grissonnanche The nature of the pseudogap phase of cuprates remains a major puzzle. Although there are indications that this phase breaks various symmetries, there is no consensus on its fundamental nature [1]. |
Monday, March 2, 2020 9:48AM - 10:24AM |
A67.00004: Thermal Hall effect in quantum paramagnets and cuprates Invited Speaker: Jung Hoon Han Several theoretical aspects of thermal Hall transport in magnetic insulators are discussed in light of recent experimental progress in frustrated magnets and in undoped cuprates. A general formalism for calculating thermal Hall conductivity in magnets is presented[1,2] and used to compute such quantity for kagome ferromagnets[1] and antiferromagnets[3] under the perpendicular magnetic field. Both calculations bear close resemblance to actual experimental data. Furthermore I discuss our recent theoretical effort to understand the remarkable yet puzzling observation of large thermal Hall conductivity in undoped to lightly doped cuprates[4]. A tentative scenario in terms of spinon Fermi surface is presented to work, to a certain extent, in matching the observation, albeit on weak experimental foundation. The talk covers materials learned from collaboration with Hyungyong Lee, Jin-Hong Park, Patrick Lee, and Yamashita group at ISSP. |
Monday, March 2, 2020 10:24AM - 11:00AM |
A67.00005: Thermal Hall effect in square-lattice spin liquids: an application to cuprates Invited Speaker: Mathias Scheurer Recent experiments [1] have revealed an enhanced thermal Hall effect in the pseudogap phase of several different cuprates compounds. The large signal even persists in the undoped system and, thus, challenges our understanding of the antiferromagnetic phase fundamentally. In this talk, I will analyze possible mechanisms that can give rise to a thermal Hall effect in the square-lattice Heisenberg antiferromagnet [2,3]. In particular, I will discuss the possibility [3] that the magnetic field drives the Néel state close to a transition to a phase where Néel order coexists with a chiral spin liquid. A spinon lattice model for this transition is shown to give rise to a large thermal Hall conductivity that also features a similar magnetic field and temperature dependence to experiment. We will derive the low-energy continuum field theory for the transition, which is characterized by an emergent global SO(3) symmetry and has four different formulations that are all related by dualities. |
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