SmB₆: A Promising Candidate for a Topological Insulator

Abstract

Three-dimensional topological insulators represent a new quantum state. They were originally proposed by a theoretical approach, but subsequently observed experimentally, e.g., in Bi 1- x Sb x and Bi 2- x Y x X 3 with X=Se and Y=Ca as well as X=Te and Y=Sn. A characteristic feature is the existence of metallic surface states with an odd number of Dirac points, which are protected by the time reversal symmetry. Furthermore, it was also suggested that some of the so-called Kondo insulators might be topological insulators. Here, we predict on the basis of calculations of topological indices and of spectrum of surface states of a detailed model, that SmB 6 should indeed be a strong topological insulator. We suggest that the metallic surface states of this strong topological insulator are hitherto unexplained in-gap states. Note that, to distiguish it from the systems mentioned above, SmB 6 is a stoichiometric compound.