Superconductivity in two-band systems with variable charge carrier density. The case of MgB2

TL;DR

This paper develops a theoretical model for two-band superconductors like MgB2, analyzing how charge carrier density variations affect critical temperature, energy gaps, and specific heat, aligning with experimental observations.

Contribution

It introduces a theory incorporating charge doping effects and impurity scattering to explain thermodynamic properties of MgB2.

Findings

Tc and energy gaps decrease with electron doping

Doping with holes causes minimal change in properties

Inter- and intraband scattering improve theoretical-experimental agreement

Abstract

The theory of thermodynamic properties of two-band superconductor with reduced density charge carriers is developed on the base of phonon superconducting mechanism with strong electron-phonon interaction. This theory is adapted to describe the behavior of critical temperature Tc, energy gaps Delta1, Delta2, and the relative jump of electron specific heat (Cs - Cn)/Cn in the point T = Tc along with the variation of charge carrier density in the compound MgB2 when substitutional impurities with different valence are introduced into the system. It is shown, that according to the filling mechanism of energy bands which overlap on Fermi surface, the quantities Tc, Delta1, Delta2 decrease when this compound is doped with electrons and remain constant or weakly change when the system is doped with holes. The theory qualitatively agrees with the experimental data. Also is shown that the consideration of inter- and intraband scattering of electrons on impurity potential improves this agreement.