Bipolarons and superconductivity

Abstract

Bipolarons in crystalline structures can undergo a superfluid phase transition similar to the one in 4He II. The order parameter of the condensate state is the phase of the bipolaronic wavefunction on a given lattice site. The phase fluctuations in bipolaronic superconductors, which are of collective nature, are compared to those in BCS superconductors which are not. The main characteristic differences in the thermodynamic quantities between those two types of superconductivity are highlighted in order to give a guide line for possible experimental verification of bipolaronic superconductivity.