Thermoelectric transport properties of surface states in three-dimensional topological insulator film

Abstract

We study the thermoelectric properties of surface states in three-dimensional topological
insulator film. The typical Seebeck and Nernst effects are numerically investigated. As the surface
states lie in the quantum spin Hall phase, the Seebeck coefficient Sc is an odd function of Fermi
energy while the Nernst coefficient Nc is an even function. Sc and Nc show peaks when the
Fermi energy crosses different propagating modes. Under the magnetic field, some abnormal peaks
appear in Sc due to the exotic hump-shape energy band. By magnetically doping the film, the
quantum anomalous Hall states dominate the system transport, the Seebeck coefficient remains
an odd function at zero magnetic field. However, when a magnetic field is applied, it breaks
the electron-hole symmetry, the parity of Seebeck and Nernst coefficients is disrupted.
With the emergence of the quantum pseudospin Hall phase, two huge peaks generate in the Seebeck
and Nernst coefficients. Furthermore, it is found that a strong magnetic field can open the band
gap, which can distinguish the contributions of electrons and holes to the Seebeck and Nernst effects.