Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B15: Chiral Phonons in Quantum MaterialsInvited Live Streamed
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Sponsoring Units: DCMP Chair: Steven Kivelson, Stanford University Room: McCormick Place W-183C |
Monday, March 14, 2022 11:30AM - 12:06PM |
B15.00001: Chiral phonons in 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 14, 2022 12:06PM - 12:42PM |
B15.00002: Thermal Hall effect of Kitaev quantum spin liquid candidate materials Invited Speaker: Christian Hess α-RuCl3 represents one of the most intriguing quantum materials of the past years. Numerous evidence for a significant Kitaev interaction between the j=1/2 moments which are located at the vertices of a honeycomb lattice has nourished hope to find fingerprints of the celebrated Kitaev model in this compound. Indeed, reports of a half-quantized thermal Hall effect in α-RuCl3 seem to match perfectly with the predicted thermal transport due to an emergent Majorana edge mode of the Kitaev quantum spin liquid (QSL). On the other hand, we have demonstrated that the longitudinal thermal transport of α-RuCl3 is due to phonons and is determined by a strong phonon-spin scattering. Interestingly, its temperature dependence is very similar to that of the thermal Hall conductivity which suggests the possibility of an alternative phononic scenario for the thermal Hall effect. Recently, Na2Co2TeO6 emerged as a new and interesting candidate materials for a Kitaev QSL. Our data for the longitudinal thermal conductivity reveal a striking similarity to that of α-RuCl3, as well as a large thermal Hall effect. Thus, with these two materials at hand, one can hope to obtain fresh information as to whether the thermal Hall effect in the Kitaev QSL compounds is due to genuine Majorana heat transport or due to to phonons. |
Monday, March 14, 2022 12:42PM - 1:18PM |
B15.00003: Phonon thermal Hall effect in undoped and doped strontium titanate Invited Speaker: Kamran Behnia We present a study of thermal Hall conductivity in strontium titanate, a non-magnetic insulator known to be a quantum paralectric. A sizeable thermal Hall effect is detectable and iits phononic origin appears obvious. Upon substitituation with Ca and syabilization of a ferroelectric ground state, the effect is drastically damped. On the other hand, introduction of oxygen vacancies, which makes the sytem a metal greatly enhaces the signal. The analysis of the latter case points to a phonon-electron mutual drag mecahnism, generating a novel contribution in addition to the phononic and electronic terms. The combination of the phonon dominance in energy transport with the large Hall angle of electrons and frequent momentum exchange between electrons and phonons generates a trasnverse thermal gradient , larger than what electrons and phonons alone can produce. |
Monday, March 14, 2022 1:18PM - 1:54PM |
B15.00004: Charged defects and phonon Hall effects in ionic crystals Invited Speaker: Benedetta Flebus It has been known for decades that a magnetic field can deflect phonons as they flow in response to a thermal gradient, producing a thermal Hall effect. Several recent experiments have revealed ratios of the phonon Hall conductivity κH to the phonon longitudinal conductivity κL in oxide dielectrics that are larger than 10−3 when phonon mean-free paths exceed phonon wavelengths. At the same time, κH/κL is not strongly temperature-dependent. We argue that these two properties together imply a mechanism related to phonon scattering from defects that break time-reversal symmetry, and we show that Lorentz forces acting on charged defects produce substantial skew-scattering amplitudes and related thermal Hall effects that are consistent with recent observations. |
Monday, March 14, 2022 1:54PM - 2:30PM |
B15.00005: Two mechanisms for enhanced thermal Hall effect: ferroelectric fluctuations & resonant scattering Invited Speaker: Xiao-Qi Sun In the context of recent experimental observations of an unusually large thermal Hall conductivity in insulating materials, in this talk we explore theoretical conditions under which acoustic phonons can give rise to the large effect. We will discuss two mechanisms that can be important. In the first part, we will show that the coupling of phonons to the magnetic field can be greatly enhanced in certain nearly ferroelectric insulators. We further provide a phenomenological model of extrinsic phonon thermal Hall effects that explains the SrTiO3 experiment. In the second part, we will discuss the extrinsic mechanism of resonant skew scattering, which can be a fundamental ingredient for the enhanced extrinsic thermal Hall effect in more general materials. |
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