Critical fixed points in class D superconductors

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 noninteracting 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 the critical line, separating two localized phases, there exists 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.