Interaction-mediated surface state instability in disordered three-dimensional topological superconductors with spin SU(2) symmetry

TL;DR

This paper demonstrates that weak interactions destabilize the surface states of 3D topological superconductors with spin SU(2) symmetry under disorder, leading to spontaneous time-reversal symmetry breaking and potential magnetic or insulating phases.

Contribution

It reveals that disorder-induced multifractality causes instability of surface states, resulting in spontaneous symmetry breaking in a previously topologically protected phase.

Findings

Weak interactions destabilize surface states

Disorder-induced multifractality drives instability

Surface states break time-reversal symmetry

Abstract

We show that arbitrarily weak interparticle interactions destabilize the surface states of 3D topological superconductors with spin SU(2) invariance (symmetry class CI), in the presence of non-magnetic disorder. The conduit for the instability is disorder-induced wavefunction multifractality. We argue that time-reversal symmetry breaks spontaneously at the surface, so that topologically-protected states do not exist for this class. The interaction-stabilized surface phase is expected to exhibit ferromagnetic order, or to reside in an insulating plateau of the spin quantum Hall effect.