Enhanced Andreev scattering by order-disorder transitions in short coherence length superconductors

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Abstract
The authors predict that the excitations of a superconductor with a spatially inhomogeneous order parameter Delta (r) can be localised by Andreev scattering. Results of calculations on two models are presented. The first contains fluctuations only in the magnitude of Delta (r), while the second has fluctuations only in the phase of Delta (r). For both models, the authors' results suggest that all quasi-particle states are localised in one dimension. In particular they show that for quasi-particles incident on the superconductor from a normal wire, the reflection coefficient for Andreev scattering can approach unity, even for energies far above the maximum value of mod Delta (r) mod . This leads to new charging effects which can be used as an experimental probe for order-disorder transitions in Delta (r).