Two-dimensional thermoelectrics with Rashba spin-split bands in bulk BiTeI

The Rashba effect is interesting for thermoelectrics because of the unique spin-splitting band structure. By using bulk BiTeI with a giant Rashba effect as an example, we prove that the spin-splitting-induced constant density of states leads to a two-dimensional thermopower. The thermopower is higher as compared with that in spin-degenerate bands, primarily due to the lower Fermi level in the Rashba spin-splitting bands at given carrier concentrations. A quantitative relation between thermopower and the Rashba parameter is established. Furthermore, the internal electric field in the Rashba system can be beneficial to bond anharmonicity and low lattice thermal conductivity. We suggest that bulk materials with large Rashba effect may become potential candidates for efficient thermoelectricity.