Surface transport coefficients for three-dimensional topological superconductors

TL;DR

This paper demonstrates that surface spin and thermal conductivities in three-dimensional topological superconductors are universal, quantized, and unaffected by localization or interaction corrections due to symmetry protections.

Contribution

It provides a theoretical proof that surface transport coefficients are topologically quantized and immune to localization and interaction effects in 3D topological superconductors.

Findings

Surface conductivities are universal and quantized.

Localization corrections vanish due to time-reversal symmetry.

Interaction corrections are suppressed by symmetry constraints.

Abstract

We argue that surface spin and thermal conductivities of three-dimensional topological superconductors are universal and topologically quantized at low temperature. For a bulk winding number $\nu$, there are $|\nu|$ "colors" of surface Majorana fermions. Localization corrections to surface transport coefficients vanish due to time-reversal symmetry (TRS). We argue that Altshuler-Aronov interaction corrections vanish because TRS forbids color or spin Friedel oscillations. We confirm this within a perturbative expansion in the interactions, and to lowest order in a large-$|\nu|$ expansion. In both cases, we employ an asymptotically exact treatment of quenched disorder effects that exploits the chiral character unique to two-dimensional, time-reversal-invariant Majorana surface states.