Kramers doublet ground state in topological Kondo insulators

Abstract

We consider the simplest variant of a Kondo insulator where a doublet of localized $f$-electrons hybridizes with spin-degenerate conduction electrons. We analyse the symmetries of $f$-orbitals involved in the hybridization and point out that the effective four-band model of such systems is adiabatically connected with one that possesses chiral symmetry, which provides further descriptions of clean Kondo insulators. We obtain general conditions for the appearance of topological non-trivial states and discuss implications for rare-earth based compounds. As an example, we derive the full phase diagram of tetragonal Kondo insulators. We show that the chiral symmetry leads to a non-trivial topological phase when the band-width of conduction electrons sets the largest energy scale, and a new weak topological phase appears as function of the normalized distance between bands' centers.