Resonating mean-field theoretical approach to two-gap superconductivity with high-Tc

Abstract

In the recent paper (referred to as I), the resonating mean-field theory (Res-MFT) has been applied and shown to effectively describe the so-called two-gap superconductivity (SC). In I, a state with large quantum fluctuations has been approximated by superposition of two MF wave functions composed of Hartree-Bogoliubov (HB) wave functions with different correlation structures. Particularly in I, using a suitable chemical potential, at T=0 the two-gap SC in MgB2 has been well described by the Res-HBT. Furthermore the Res-HB ground state generated with HB wave functions has almost explained value of the ground-state correlation energy in all the correlation regimes including an intermediate coupling regime. In the present paper we will apply the Res-HBT to the two-gap SC with high critical temperature Tc. We will aim at constructing a theoretical foundation for phenomenological theories of the two-gap SC at T=0 and finite temperature. In the single-gap case we will find a new formula leading to a higher Tc than the usual HB's.