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Title: Origin of the large phonon thermal Hall effect in cuprates
Plain: In copper-oxide superconductors, phonons gain a large sideways heat flow below the doping where the pseudogap state appears and also in the undoped insulating parents. What gives phonons this handedness is unknown.
Precise: In hole-doped cuprates inside the pseudogap phase and in the Mott insulators La2CuO4 and Sr2CuO2Cl2, a large negative $\kappa_{xy}$, present for heat flow both in the CuO2 planes and along $c$, is attributed to phonons (Grissonnanche et al. 2019, 2020); a planar thermal Hall response with $B$ in the plane was reported in 2024 (Chen et al., Physical Review X 14, 041011). Identify what couples phonons to $B$ (spin fluctuations of the antiferromagnetic background, defects, or charge-order domains) and predict the doping, field-direction and temperature dependence.
Settled by: A microscopic coupling that predicts doping, field-direction and temperature dependence, checked across hole- and electron-doped cuprates and across defect densities.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: open
Status note: (empty)
Posed since: 2019