Metallicity in a correlated topologically ordered system, SmB6

We have performed the electronic structure calculations of SmB6 within the framework of density functional theory using the full potential linearized augmented-plane wave (FP-LAPW) approach as implemented in the WIEN2k package. Within the generalized gradient approximation (GGA), it is found that there are a large number of Sm 4f states at the Fermi energy (E-F), which shows the metallic nature of SmB6. With the application of spin orbit coupling (SOC), there is a dramatic decrease in the Density of states (DOS) at EF akin to a pseudogap like feature. Further, the Sm 4f states split into j = 5/2 states appearing below E-F, and j = 7/2 states above E-F. In order to verify the robustness of the low energy band topology, we have also applied the modified Becke Johnson (mBJ) exchange potential incorporating SOC and found that the pseudogap feature is still present in the electronic structure suggesting metallicity of the bulk electronic structure. The results from GGA, GGA+SOC and mBJ+SOC calculations establish that the DOS near the EF is primarily contributed by Sm 4f states with some contribution from Sm 5d eg and B 2p states. Our findings could explain the bulk fermi surface observed in quantum oscillation measurements of SmB6.