A new exotic state in an old material: A tale of Samarium Hexaboride

TL;DR

This paper reviews the theoretical and experimental progress in understanding topological Kondo insulators, focusing on materials like Samarium Hexaboride, which exhibit a bulk insulating state with metallic surface states due to band inversion effects.

Contribution

It provides a comprehensive overview of the mechanisms behind topological Kondo insulators, highlighting the role of band inversion and symmetry in their exotic surface states.

Findings

Identification of band inversion as key to surface metallicity

Chiral surface states are robust against disorder

Experimental challenges in probing surface states

Abstract

We review current theoretical and experimental efforts to identify a novel class of intermetallic 4f and 5f orbital materials in which strong interactions between itinerant and predominately localized degrees of freedom gives rise to a bulk insulating state at low temperatures, while the surface remains metallic. This effect arises due to inversion of even parity conduction bands and odd parity very narrow f-electron bands. The number of band inversions is mainly determined by the crystal symmetry of a material and the corresponding degeneracy of the hybridized f-electron bands. For odd number of band inversions the metallic surface states are chiral and therefore remain robust against disorder and time-reversal invariant perturbations. We discuss a number of unresolved theoretical issues specific to topological Kondo insulators and outline experimental challenges in probing the chiral surface states in these materials.