What do the phase-sensitive experiments tell us?

Abstract

The phase-sensitive experiments on cuprate superconductors have told us about the symmetry of the condensate wavefunction. However, they can not determine the pairing symmetry of Cooper pairs. To describe a superconducting state, two wavefunctions are needed, condensate wavefunction and pairing wavefunction. The former describes the entirety movement of the pairs and the latter describes the relative movement of the two electrons within a pair. The $π$-phase shift observed in the phase sensitive Josephson measurements can not prove that the pairing state is d-wave. We present here a new explanation and predict some new observable phenomena.