Current Correlations in Strongly Disordered Superconductors

We calculate the current response to a static vector potential in disordered superconductors. In contrast to standard BCS theory which violates gauge invariance, it is important here to incorporate the coupling to phase fluctuations in order to obey charge conservation. At strong disorder, where the system breaks up into superconducting islands, the superfluid stiffness is determined by percolative current paths which form via a 'constriction' process from the homogeneous situation.