Recovery of superconductivity and the critical field in layered superconductors

The presence of magnetic impurities greatly affects the temperature dependence of the critical field Hc2. We focus, mainly, on layered superconductors. As a result of correlations among magnetic impurities, the scattering amplitude Γₛ decreased with T{→}0 K. This temperature dependence leads to a weakening of the pair-breaking effect and consequently to a positive curvature of Hc2(T) and a drastic increase in Hc2(0). The calculations are in excellent agreement with recent experimental data. It is also shown that the presence of inhomogeneities of a certain size also modifies the temperature dependence of Hc2. {} 1996 The American Physical Society.