Multiple phases in a new statistical boson-fermion model of superconductivity

Abstract

We apply a new statistical complete boson-fermion model (CBFM) to describe superconductivity with arbitrary departure from the perfect two-electron (2e) and two-hole (2h) Cooper pair (CP) symmetry to which BCS theory is restricted. The model is complete in that it accounts for both 2h and 2e CPs. In special cases the CBFM reduces to all the main statistical continuum models of superconductivity. From it four stable thermodynamic phases emerge around the BCS state, a normal and three stable Bose-Einstein condensed phases of which one is mixed (with both CP types) and two pure. Critical temperatures T-c for the new pure phases rise as one departs from the mixed BCS state, and can result in substantially higher T-c's than with BCS theory for moderate departures from perfect 2e/2h CP symmetry. (C) 2003 Elsevier Science B.V. All rights reserved.