Transport properties of extended-s-state superconductors

Superconducting states with extended-s-wave symmetry have been suggested in connection with recent angle-resolved photoemission experiments on ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$. In the presence of impurities, thermodynamic properties of such states reflect a residual density of states N(0) for a range of concentrations. While properties reflecting N(ω) alone will be similar to those of d-wave states, transport measurements may be shown to distinguish qualitatively between the two. In contrast to the d-wave case with unitarity limit scattering, limiting low-temperature residual conductivities in the s-wave state are large and scale inversely with impurity concentration.