Lower Bound for the Fermi Level Density of States of a Disordered D-Wave Superconductor in Two Dimensions

TL;DR

This paper establishes a nonzero lower bound for the Fermi level density of states in disordered two-dimensional d-wave superconductors, demonstrating the result's robustness across various disorder distributions.

Contribution

It extends previous exact results for Lorentzian disorder to a broad class of distributions, showing the nonzero density of states is a generic feature.

Findings

Nonzero lower bound for density of states established

Result holds for Gaussian and other distributions

Exact Lorentzian case is representative of general behavior

Abstract

We consider a disordered d--wave superconductor in two dimensions. Recently, we have shown in an exact calculation that for a lattice model with a Lorentzian distributed random chemical potential the quasiparticle density of states at the Fermi level is nonzero. As the exact result holds only for the special choice of the Lorentzian, we employ different methods to show that for a large class of distributions, including the Gaussian distribution, one can establish a nonzero lower bound for the Fermi level density of states. The fact that the tails of the distributions are unimportant in deriving the lower bound shows that the exact result obtained before is generic.