Nonzero Fermi Level Density of States for a Disordered d-Wave Superconductor

TL;DR

This paper demonstrates that in two-dimensional disordered d-wave superconductors, the residual density of states at zero energy remains nonzero, challenging previous models suggesting it vanishes in 2D.

Contribution

The study provides exact calculations showing nonzero residual density of states in 2D disordered d-wave superconductors, clarifying discrepancies with earlier theoretical predictions.

Findings

Residual density of states N(0) is nonzero in 2D disordered d-wave superconductors.

Exact calculations confirm the persistence of low-energy quasiparticle states.

Implications for understanding cuprate superconductors are discussed.

Abstract

It has been known for some time that, in three dimensions, arbitrarily weak disorder in unconventional superconductors with line nodes gives rise to a nonzero residual density of zero-energy quasiparticle states N(0), leading to characteristic low-temperature thermodynamic properties similar to those observed in cuprate and heavy-fermion systems. In a strictly two-dimensional model possibly appropriate for the cuprates, it has been argued that N(0) vanishes, however. We perform exact calculations for d- and extended s-wave superconductors with Lorentzian disorder and similar models with continuous disorder distribution, and show that in these cases the residual density of states is nonzero even in two dimensions. We discuss the reasons for this discrepancy, and the implications of our result for the cuprates.