Chemical potential influence on the condensation energy from a Boson-Fermion model of superconductivity

TL;DR

This paper investigates how the temperature-dependent chemical potential affects the condensation energy in a Boson-Fermion superconductivity model, revealing shifts and discontinuities that align with experimental observations.

Contribution

It introduces a detailed analysis of the chemical potential's role in condensation energy within a Boson-Fermion model, highlighting the importance of accounting for chemical potential shifts.

Findings

Chemical potential shifts significantly below T_c.

A kink in chemical potential at T_c coincides with the normal state.

Condensation energy matches experimental data for elemental superconductors.

Abstract

Influence of the temperature dependent chemical potential on the condensation energy from a ternary Boson-Fermion model of superconductivity is reported, it consist of unbound electrons/holes which are fermions plus two-electron and two-hole Cooper pairs which are bosons. When solving simultaneously the set of equations of the mixture (two gap-like equations, one for electron pairs and another one for hole pairs, plus the particle number conservation equation) within the weak-coupling (BCS regime), the resulting superconducting chemical potential shows a shift from its normal state counterpart, which is related to both the magnitude of the temperature-dependent superconducting gap and to the Fermi energy of the superconductor. As predicted by van der Marel in the early 1990s we also find that the superconducting chemical potential has a prominent kink at critical temperature $T_c$, which in turn coincides with the normal state chemical potential. Also there is discontinuity in its first derivative which directly affects the magnitude in the specific heat jump. We show that the difference between the superconducting and normal state chemical potentials is of the same order of magnitude as the corresponding difference between the thermodynamic potentials for the mixture, and must therefore be accounted for in the condensation energy calculations instead of ignoring it as is done often. The condensation energy obtained here shows very good agreement with experimental data for elemental superconductors.