Seiya Nishiyama, Joao da Providencia, Constanca Providencia, Hiromasa Ohnishi
The resonating mean-field theory (Res-MFT) has been applied and shown to effectively describe the so-called two-gap superconductivity (SC). 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 using a suitable chemical potential, at T=0 the two-gap SC in MgB2 has been well described by the Res-HBT. The Res-HB ground state generated with HB wave functions almost explains value of the ground-state correlation energy in all the correlation regimes including an intermediate coupling regime. In this paper we apply the Res-HBT to the two-gap SC with high critical-temperature Tc and aim at providing a theory for the two-gap SC at finite temperature. In the single-gap case we find a new formula leading to a higher Tc than the Tc of the usual HB formula.
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http://arxiv.org/abs/1209.4361
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