Is room-temperature superconductivity with phonons possible?

Abstract

By recognizing the vital importance of two-hole Cooper pairs (CPs) in addition to the usual two-electron ones in a strongly-interacting many-electron system, the concept of CPs was re-examined with striking conclusions. Based on this, Bose-Einstein condensation (BEC) theory has been generalized to include not boson-boson interactions (also neglected in BCS theory) but rather boson-fermion (BF)interaction vertices reminiscent of the Frohlich electron-phonon interaction in metals. Unlike BCS theory, the GBEC model is not a mean-field theory restricted to weak-coupling as it can be diagonalized exactly. In weak coupling it reproduces the BCS condensation energy. Each kind of CP is responsible for only half the condensation energy. The GBEC theory reduces to all the old known statistical theories as special cases including the so-called "BCS-Bose crossover" picture which in turn generalizes BCS theory by not assuming that the electron chemical potential equals the Fermi energy. Indeed, a BCS condensate is precisely the weak-coupling limit of a GBE condensate with equal numbers of both types of CPs. With feasible Cooper/BCS model interelectonic interaction parameter values, and even without BF interactions, the GBEC theory yields transition temperatures [including room-temperature superconductivity (RTSC)] substantially higher than the BCS ceiling of around 45K, without relying on non-phonon dynamics involving excitons, plasmons, magnons or otherwise purely-electronic mechanisms.