Higher-Order Nodal Hinge States in Doped Superconducting Topological Insulator

Understand

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.