Generic magnetic field dependence of thermal conductivity in effective spin-1/2 magnetic insulators enabled by hybridization of acoustic phonons and spin-flip excitations

We present a model for magnetic field dependence of thermal conductivity at low temperature in effective spin-1/2 magnetic insulators. We find that in a paramagnetic state (i.e. in the absence of magnetic ordering), the hybridization between acoustic phonons and the localized spin-flip-excitations across the Zeeman gap of the crystal electric field Kramers' doublet ground state is responsible for the non-monotonic field dependence of thermal conductivity . Our model successfully captures the essential features of magnetothermal conductivity of a rare earth insulating magnet, CsYbSe₂ and should be generic to any spin-1/2 systems with a suitable magnetoelastic coupling mechanism. We will discuss the limitations and implications of our model, which is expected to apply to a wide range of quantum magnets.