Thermoelectric transport in thin films of three-dimensional topological insulators

We numerically study the thermoelectric transport properties based on the Haldane model of the three-dimensional topological insulator (3DTI) thin film in the presence of an exchange field g and a hybridization gap Delta. The thermoelectric coefficients exhibit rich behaviors as a consequence of the interplay between g and Delta in the 3DTI thin film. For Delta = 0 but g not equal 0, the transverse thermoelectric conductivity alpha(xy) saturates to a universal value 1.38k(B)e/h at the center of each Landau level (LL) in the high-temperature regime, and displays a linear temperature dependence at low temperatures. The semiclassical Mott relation is found to remain valid at low temperatures. If g = 0 but Delta not equal 0, the thermoelectric coefficients are consistent with those of a band insulator. For both g not equal 0 and Delta not equal 0, alpha(xy) saturates to a universal value 0.69k(B)e/h at the center of each LL in the high-temperature regime. We attribute this behavior to the split of all the LLs, caused by the simultaneous presence of nonzero g and Delta, which lifts the degeneracies between Dirac surface states. DOI: 10.1103/PhysRevB.87.115304