Critical fixed points in class D superconductors

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 $W_T$.Comment: 3 pages, one figur