Critical fixed points in class D superconductors

TL;DR

This paper investigates the phase diagram of a disordered superconductor model, identifying critical points and fixed points that influence phase transitions and thermal Hall conductance in non-interacting quasiparticles.

Contribution

It uncovers a new repulsive fixed point in the phase diagram of the Cho-Fisher network model, revealing complex RG flow behavior in class D superconductors.

Findings

Identification of a critical line separating metallic and localized phases.

Discovery of a new repulsive fixed point W_N influencing RG flow.

Existence of a tricritical fixed point W_T on the critical line.

Abstract

We study in detail a critical line on the phase diagram of the Cho-Fisher network model separating three different phases: metallic and two distinct localized phases with different quantized thermal Hall conductances. This system describes non-interacting quasiparticles in disordered superconductors that have neither time-reversal nor spin-rotational invariance. We find that in addition to a tricritical fixed point $W_T$ on that critical line there exist an additional repulsive fixed point $W_N$ (where the vortex disorder concentration $W_N<W_T$), which splits RG flow into opposite directions: toward a clean Ising model at W=0 and toward $W_T$.