Enhancing superconductivity: Magnetic impurities and their quenching by magnetic fields

Magnetic fields and magnetic impurities are each known to suppress superconductivity. However, as the field quenches (i.e. polarizes) the impurities, rich consequences, including field-enhanced superconductivity, can emerge when both effects are present. In superconducting wires and thin films this field-spin interplay is investigated via the Eilenberger-Usadel scheme. Non-monotonic dependence of the critical current on the field (and therefore field-enhanced superconductivity) is found to be possible, even in parameter regimes for which the superconducting critical temperature decreases monotonically with increasing field. The present work complements that of Kharitonov and Feigel'man (JETP Lett., 82 (2005) 421), which predicts regimes of non-monotonic behavior of the critical temperature.