Shadow surface states in topological Kondo insulators

TL;DR

This paper demonstrates that topological Kondo insulators can host shadow surface states with large Fermi surfaces, leading to observable high-frequency quantum oscillations even when the chemical potential is at the Dirac point.

Contribution

It introduces the concept of shadow surface states in topological Kondo insulators and shows how crystal symmetry and hybridization stabilize these states, resulting in high-frequency quantum oscillations.

Findings

Shadow surface states support large Fermi surfaces at the Dirac point.

These states produce finite-frequency quantum oscillations.

Symmetry lowering from cubic to tetragonal stabilizes shadow surface states.

Abstract

The surface states of 3D topological insulators in general have negligible quantum oscillations when the chemical potential is tuned to the Dirac points. In contrast, we find that topological Kondo insulators can support surface states with an arbitrarily large Fermi surface when the chemical potential is pinned to the Dirac point. We illustrate that these Fermi surfaces give rise to finite-frequency quantum oscillations, which can become comparable to the extremal area of the unhybridized bulk bands. We show that this occurs when the crystal symmetry is lowered from cubic to tetragonal in a minimal two-orbital model. We label such surface modes as `shadow surface states'. Moreover, we show that the sufficient next-nearest neighbor out-of-plane hybridization leading to shadow surface states can be self-consistently stabilized for tetragonal topological Kondo insulators. Consequently, shadow surface states provide an important example of high-frequency quantum oscillations beyond the context of cubic topological Kondo insulators.