Thermal and thermal-Hall conductivity study of SrCu₂(BO₃)₂

We present measurements of the thermal and the thermal-Hall conductivity as a function of temperature and magnetic field in the twodimensional dimer spin system SrCu₂(BO₃)₂. The thermal conductivity in zero magnetic field shows a pronounced peak around 4 K which is ascribed to a spin-gap opening. The low-temperature maximum is strongly suppressed by the application of magnetic field. This result implies that the majority of heat is conducted by phonons which interact with the magnetic excitations. Furthermore, a theoretical study predicted a strong thermal Hall signature due to anisotropies originating from the Dzyaloshinskii-Moriya interactions which lead to a topological character of triplon excitations [1]. Our detailed experimental investigation did not reveal such effect disproving the existence of topological transitions in the triplon band structure.