Termination-dependent Surface In-gap States in a Mixed-valent Topological Insulator: SmB$_6$

TL;DR

This study uses first-principles calculations to analyze surface states in SmB$_6$, revealing termination-dependent in-gap states and confirming its topological insulator properties with spin-chiral Fermi surfaces.

Contribution

It demonstrates the termination-dependent nature of surface states in SmB$_6$ and highlights the importance of including f electrons in theoretical descriptions.

Findings

Surface states are formed in the bulk band gap region.

Surface states depend on Sm or B$_6$ surface termination.

Surface states mainly consist of Sm 4f electrons.

Abstract

We have investigated the surface states of a potential mixed-valent topological insulator SmB$_6$ based on the first principles density functional theory slab band structure analysis. We have found that metallic surface states are formed in the bulk band gap region, providing evidence for the topological insulating nature of SmB$_6$. The obtained surface in-gap states are quite different from those in existing reports in that they are formed differently depending on the Sm or B$_6$ surface termination, and are composed of mainly Sm $4f$ state indicating the essentiality of including $f$ electrons in describing the surface states. We have obtained the spin chiral structures of the Fermi surfaces, which are also in accordance with the topological insulating nature of SmB$_6$.