Thermal Hall Effect Measurements on Topological Materials

In the past few decades topology has become a central theme in condensed matter physics, allowing a more complete understanding of concepts such as the quantum Hall effect and of the class of materials termed topological insulators. Topological insulators were first predicted in 1987 and have subsequently been experimentally realised in a host of materials. A similar effect has been predicted to occur for SrCu2(BO3)2 (SCBO) but with one crucial difference; unlike those materials previously found, it is the spin waves that have a topological character rather than the conduction bands [3]. SCBO is therefore a bosonic topological material.
Theoretical predictions from [1] suggest that the topological nature of SCBO should be evident from thermal Hall effect measurements. In order to demonstrate the feasibility of these measurements, we have used our setup to reproduce those results from [2], which show a (magnon) Hall effect signal of a similar magnitude to that predicted for SCBO, and under similar conditions. We then present new thermal Hall data on the material SCBO, for which a positive result would be evidence for one of the first known bosonic topological insulators.

[1] P. A. McClarty et al. Nat Phys,13, 736–741 (2017).
[2] Y. Onose et al. Science, 329, 297 (2010).