Thermal Hall Conductivity of Electron Doped Cuprates

Measurements of the thermal Hall conductivity in hole-doped cuprates showed that phonons acquire chirality in a magnetic field, both in the pseudogap phase [1,2] and in the Mott insulator state [3]. The microscopic mechanism at play is still unclear. A number of theoretical proposals are being considered, including skew scattering of phonons by various defects [4,5,6], the coupling of phonons to spins [7] and a state of loop-current order with the appropriate symmetries [8]. But more experimental information is required. 

Here we present our study of the thermal Hall conductivity in the electron-doped cuprates Nd_2-xCe_xCuO₄ and Pr_2-xCe_xCuO₄, for dopings across the phase diagram, from x = 0, in the insulating antiferromagnetic phase, up to x = 0.17, in the metallic phase above optimal doping. We observe a large negative thermal Hall conductivity at all dopings, in both materials. Measurements with a heat current perpendicular to the CuO₂ planes confirm that phonons are responsible for this thermal Hall signal, as in hole-doped cuprates. We discuss the possibility that short-range spin correlations may be involved in the mechanism that confers chirality to the phonons.