DISTINGUISHING D-WAVE SUPERCONDUCTORS FROM HIGHLY ANISOTROPIC S-WAVE SUPERCONDUCTORS

Systematic impurity doping in the Cu-0 plane of the hole-doped cuprate superconductors may allow one to decide between unconventional (''d-w ave'') and anisotropic conventional (''s-wave'') states as possible ca ndidates for the order parameter in these materials. We show that pote ntial scattering of any strength always increases the gap minima of su ch s-wave states, leading to activated behavior in temperature with ch aracteristic impurity concentration dependence in observable quantitie s such as the penetration depth. A magnetic component to the scatterin g may destroy the energy gap and give rise to conventional gapless beh avior, or lead to a nonmonotonic dependence of the gap on impurity con centration. We discuss how experiments constrain this analysis.