Higher-Order Nodal Hinge States in Doped Superconducting Topological Insulator

TL;DR

This paper uncovers the existence of higher-order topological hinge states in doped superconducting topological insulators, revealing new possibilities for realizing Majorana modes in these materials.

Contribution

It demonstrates the emergence of higher-order topology and hinge states in doped topological insulators with superconductivity, a feature previously overlooked in this class of materials.

Findings

Hinge states coexist with surface states under certain doping conditions.

Hinge modes can appear in doped strong or weak topological insulators.

Superconducting hinge modes are linked to the presence of both bulk and surface Fermi-surfaces.

Abstract

Doped strong topological insulators are one of the most promising candidates to realize a fully gapped three-dimensional topological superconductor (TSC). In this letter, we revisit this system and reveal a possibility for higher-order topology which was previously missed. We find that over a finite-range of doping, the Fu-Berg superconducting pairing can give rise to both Majorana surface states, and nodal hinge states. Interestingly, we observe the coexistence of surface and hinge modes in the superconducting state only when there are both bulk and surface Fermi-surfaces in the normal state. Also, we find that the hinge modes can appear for normal states consisting of doped strong or weak topological insulators. In summary, this work may allow for the discovery of superconducting hinge modes in a well explored class of materials, i.e., doped strong or weak topological insulators.