Romhányi Judit - Thermal Hall effect in SrCu2(BO3)2
We show that SrCu2(BO3)2 (SCBO), the well known realization of the Shastry Sutherland model, hosts topological triplon bands. The Shastry Sutherland model has an exact dimer singlet ground state.
However, the material SCBO has small Dzyaloshinskii-Moriya (DM) interactions which admix a triplet component into the ground state. The lowest excitations are three gapped triplon modes, well described by bond wave theory. An applied magnetic ﬁeld opens band gaps and surprisingly, we are left with topological bands characterized by non-zero (±2) Chern numbers. Thus, SCBO supports protected triplonic edge modes and is a magnetic analogue of the integer quantum Hall eﬀect.
Ultimately, this topological character stems from the DM interactions which generate a Lorentz force for triplons. Our results may be veriﬁed by thermal Hall measurements.