Seminar "Thermal Hall effect from neutral currents in quantum magnets" by Dr. Max Hirschberger

Speaker

Dr. Max Hirschberger from RIKEN Center for Emergent Matter Science

Title

Thermal Hall effect from neutral currents in quantum magnets

Abstract

The thermal conductivity kappa_xx of spin excitations in magnetic insulators can be large at low temperatures, swamping the contribution of phonons. In this regime, theory predicts that in some lattice geometries, Berry curvature leads to an effective transverse force acting on heat carriers, akin to a Lorentz force (for neutral particles). In this seminar, we discuss the observation of this thermal Hall conductivity kappa_xy in a ferromagnetic insulator and in the paramagnetic regime of two rare earth pyrochlore titanate compounds with frustrated exchange interactions. We show that although phonons may in principle contribute to kappa_xy, their signal is small in the present cases. Finally, we summarize other recent experimental and theoretical advances in this field.