Thermal Hall effect in quantum paramagnets and cuprates

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.

[1] “Thermal Hall effect of spins in a paramagnet", Hyunyong Lee, Jung Hoon
Han, and Patrick A. Lee, Phys. Rev. B 91, 125413 (2015).
[2] “Spin Chirality and Hall-Like Transport Phenomena of Spin Excitations",
Jung Hoon Han, and Hyunyong Lee, J. Phys. Soc. Jpn. 86, 011007
(2017).
[3] “Spin Thermal Hall Conductivity of a Kagome Antiferromagnet", Hayato
Doki et al., Phys. Rev. Lett. 121, 097203 (2018).
[4] “Consideration of thermal Hall effect in undoped cuprates", Jung Hoon
Han, Jin-Hong Park, and Patrick A. Lee, Phys. Rev. B 99, 205157 (2019).