Microscopic free energy functional of superconductive amplitude and phase: Superfluid density in disordered superconductors
Abstract
Recent experiments on disordered superconductors find that the superfluid density ns(T) decreases dramatically and characteristically with disorder, differently from what is expected for a mean order parameter field or BCS, amplitude only, picture for the superconductor. We describe here a new microscopic free energy functional which explicitly describes its dependence on both the amplitude and phase of superconducting order, in a gauge invariant manner. We use this here in an approximation of noninteracting phase fluctuations (Gaussian or harmonic approximation) to obtain ns(T) in the presence of (static) disorder. We compare our results successfully with experiment.
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