Acoustic phonon dispersion of α-RuCl3

Acoustic phonons have recently been posited as playing an integral role in explaining the half-quantized thermal Hall effect in α-RuCl3. Therefore, we present much needed inelastic X-ray scattering measurements of its acoustic phonon dispersion, along with calculations using the frozen-phonon method. We also discuss a temperature study which conclusively shows a first-order structural transition to a non-C2/m space group at low temperature. Together these results are an important backbone for future theoretical and experimental studies of α-RuCl3. © 2022 American Physical Society. Office of Science, SC; Argonne National Laboratory, ANL: DE-AC02-06CH11357; Ontario Innovation Trust, OIT; Natural Sciences and Engineering Research Council of Canada, NSERC; Canada Foundation for Innovation, CFI; Deutsche Forschungsgemeinschaft, DFG: 107745057, TRR80; University of Toronto, U of T; Russian Science Foundation, RSF: 21-72-10136 Work at the University of Toronto was supported by the Natural Science and Engineering Research Council (NSERC) of Canada, Canadian Foundation for Innovation, and Ontario Innovation Trust. This research used resources of the Advanced Photon Source (APS), a DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. B.W.L. acknowledges support from the University of Toronto Faculty of Arts and Sciences Postdoctoral Fellowship and NSERC (funding reference number PDF-546035-2020). The work of D.A.P. was supported by the Russian Science Foundation, Grant No. 21-72-10136. The work in Augsburg was supported by the German Research Foundation (DFG) via Project No. 107745057 (TRR80).