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 Materials
11:30 AM–2:30 PM,
Monday, March 14, 2022
Room: McCormick Place W-183C
Sponsoring Unit: DCMP
Chair: Steven Kivelson, Stanford University
Abstract: B15.00001 : Chiral phonons in cuprate superconductors
11:30 AM–12:06 PM
Here we report measurements of the thermal Hall conductivity κxy in the normal state of four different cuprates and show that a large negative κxy signal is a property of the pseudogap phase, appearing with the onset of that phase at the critical doping p*. It is also a property of the Mott insulator at p ≈ 0, where κxy has the largest reported magnitude of any insulator. Since this negative κxy signal grows as the system becomes increasingly insulating electrically, it cannot be attributed to conventional mobile charge carriers. Nor is it due to magnons, since it exists in the absence of magnetic order.
In order to identify the heat carriers responsible for this negative κxy, we turn to transverse heat transport along the c-axis: κzy. Here we show that the thermal Hall conductivity at p = 0 is roughly isotropic, being nearly the same for heat transport parallel and normal to the CuO2 planes, i.e. κzy(T) ≈ κxy(T). This shows that the negative thermal Hall response must come from phonons, these being the only heat carriers able to move as easily normal and parallel to the planes. At p > p*, we observe no c-axis Hall signal, i.e. κzy(T) = 0, showing that phonons have zero Hall response outside the pseudogap phase. The microscopic mechanism by which phonons become chiral in cuprates remains to be identified. This phonon Hall effect provides a new window on quantum materials and it may explain the thermal Hall signal observed in other topologically nontrivial insulators .
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 Grissonnanche et al., Nature 571, 376 (2019).
 Grissonnanche et al., Nature Physics 16, 1108 (2020).
 Kasahara et al., Nature 559, 227 (2018).
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