Edge currents as a signature of flat bands in topological superconductors

TL;DR

This paper demonstrates that edge currents in noncentrosymmetric topological superconductors, arising from flat bands, can serve as signatures of their topological surface states, with potential experimental implications.

Contribution

It reveals that nondegenerate flat bands produce strong, spin-polarized edge currents that depend singularly on exchange fields, providing a new way to detect topological flat bands.

Findings

Flat bands are strongly spin polarized.

Edge currents depend singularly on exchange-field strength.

Observation of edge currents indicates presence of flat bands.

Abstract

We study nondegenerate flat bands at the surfaces of noncentrosymmetric topological superconductors by exact diagonalization of Bogoliubov-de Gennes Hamiltonians. We show that these states are strongly spin polarized, and acquire a chiral dispersion when placed in contact with a ferromagnetic insulator. This chiral mode carries a large edge current which displays a singular dependence on the exchange-field strength. The contribution of other edge states to the current is comparably weak. We hence propose that the observation of the edge current can serve as a test of the presence of nondegenerate flat bands.