Thermal Hall conductivity in the cuprate Mott insulators Nd(2)CuO(4) and Sr(2)CuO(2)Cl(2)

The heat carriers responsible for the unexpectedly large thermal Hall conductivity of the cuprate Mott insulator La(2)CuO(4) were recently shown to be phonons. However, the mechanism by which phonons in cuprates acquire chirality in a magnetic field is still unknown. Here, we report a similar thermal Hall conductivity in two cuprate Mott insulators with significantly different crystal structures and magnetic orders – Nd(2)CuO(4) and Sr(2)CuO(2)Cl(2) – and show that two potential mechanisms can be excluded – the scattering of phonons by rare-earth impurities and by structural domains. Our comparative study further reveals that orthorhombicity, apical oxygens, the tilting of oxygen octahedra and the canting of spins out of the CuO(2) planes are not essential to the mechanism of chirality. Our findings point to a chiral mechanism coming from a coupling of acoustic phonons to the intrinsic excitations of the CuO(2) planes.