The density of states in unconventional superconductors, ${\mathit{N}}_{\mathit{s}}$(E), is very sensitive to impurity scattering, especially at low energies. We investigate the behavior of ${\mathit{N}}_{\mathit{s}}$(E), using both numerical calculations and analytic approximations; we discuss the Born limit, the unitarity limit, and the crossover between these two cases. We consider a two-dimensional electron gas with a d-wave order parameter of the form Δ(k^)=Δ(k${\mathrm{^}}_{\mathit{x}}^2$-k${\mathrm{^}}_{\mathit{y}}^2$). The low-energy structure in ${\mathit{N}}_{\mathit{s}}$(E) should be quite general, applying to all gaps with the same general behavior.

• Received 31 January 1994

DOI:https://doi.org/10.1103/PhysRevB.50.1259