Theory of giant and nil proximity effects in cuprate semiconductors

A number of observations point to the possibility that high-Tc cuprate superconductors may not be conventional Bardeen-Cooper-Schrieffer (BCS) superconductors, but rather derive from the Bose-Einstein condensation (BEC) of real-space pairs, which are mobile small bipolarons. A solution of the Gross-Pitaevskii equation describing bose-condensate tunnelling into a cuprate semiconductor is analytically found. It accounts qualitatively and quantitatively for nil and giant proximity effects discovered experimentally in cuprates.