Band Symmetries of Mixed-Valence Topological Insulator: SmB6

Abstract

We have investigated the band structure and the band symmetry of mixed-valence insulator SmB6 systematically within the density functional theory (DFT). To describe the strong correlation effect of 4 f-electrons in SmB6 effectively within the DFT level, we have devised a scheme to adjust the spin-orbit coupling (SOC) strength of Sm 4f electron artificially, which is verified to be a valid approximation by comparison with the band structure from the dynamical mean-field theory (DMFT). We have analyzed the symmetries and characters of Sm 4f and 5d bands near the Fermi level (E-F) in terms of the non-relativistic real cubic bases as well as the relativistic complex bases incorporating the SOC and the cubic crystal field. Based on the full band symmetry analysis, the ground state of SmB6 is found to be in the Gamma(7) multiplet state, and Sm 5d band that hybridizes with Sm 4f band near E-F has the e(g) symmetry. Further, we have found that the semi-core band located at similar to 15 eV below E-F has the mixed parity and thereby affects the parity eigenvalues of the special k-points considerably. We have discussed the possible surface states and topological class of SmB6, based on the bulk parity tables.