Spontaneous time-reversal symmetry breaking in the boundary Majorana flat bands

TL;DR

This paper investigates how boundary Majorana flat bands in p-wave topological superconductors spontaneously break time-reversal symmetry due to instabilities caused by divergent density of states, leading to observable current loops.

Contribution

It reveals a mechanism for spontaneous time-reversal symmetry breaking in boundary Majorana modes caused by phase variations in Cooper pairing.

Findings

Boundary Majorana flat bands are unstable against phase variations.

Spontaneous current loops form near the boundary.

Time-reversal symmetry is spontaneously broken in the orbital channel.

Abstract

We study the boundary Majorana modes for the single component p-wave weak topological superconductors or superfluids, which form zero energy flat bands protected by time-reversal symmetry in the orbital channel. However, due to the divergence of density of states, the band flatness of the edge Majorana modes is unstable under spontaneously generated spatial variations of Cooper pairing phases. Staggered current loops appear near the boundary and thus time-reversal symmetry is spontaneously broken in the orbital channel. This effect can appear in both condensed matter and ultra-cold atom systems.