π-flux Dirac Triplon and Thermal Hall Effect in Shastry-Sutherland model

SrCu2(BO3)2 provides an excellent platform for studying Shastry-Sutherland model and topological triplon excitation. In this letter, we introduce a effective 2-dimer tight-binding model to reveal significant physical observable when pseudospin (two sublattices) couples the tilted external magnetic field. The calculated band diagram holds a 2-fold degenerate Dirac triplon excitation at the Brillouin zone center (k = 0) by in-plane component part of the magnetic field. We identify this elementary excitation as having nontrivial topological properties with π-Berry flux. Using the effective Hamiltonian built based on tight-binding model, we reveals the role of in-plane magnetic field, which gives rise to Rashba pseudospin-orbit coupling term. Further, an out-of-plane component of magnetic gaps the excitation spectrum resulting in a nonzero Berry curvature hot spot around the Brillouin zone center. Using a comprehensive 2-dimer theoretical model, we also show the pronounced experimental signature for exotic nontrivial transport-the thermal Hall effect based on the gapped Dirac triplon bands.