Mutual influence of structural distortion and superconductivity in systems with degenerate bands

TL;DR

This paper investigates how structural distortions and superconductivity influence each other in systems with degenerate bands, revealing limited coexistence, the impact on transition temperatures, and agreement with experimental data on cuprates.

Contribution

It provides a theoretical phase diagram showing the interplay between Jahn-Teller distortion and BCS superconductivity in degenerate band systems.

Findings

Coexistence of superconductivity and distortion occurs within limited doping range.

Distortion lowers the superconducting transition temperature $T_c$.

Maximum $T_c$ is limited by structural transition temperature $T_s$.

Abstract

The interplay between the band Jahn-Teller distortion and the superconductivity is studied for the system whose Fermi level lies in two-fold degenerate band. Assuming that the lattice distortion is coupled to the orbital electron density and the superconductivity arises due to BCS pairing mechanism between the electrons, the phase diagram is obtained for different doping with respect to half-filled band situation. The coexistence phase of superconductivity and distortion occurs within limited range of doping and the distortion lowers the superconducting transition temperature $T_c$. In presence of strong electron-lattice interaction the lattice strain is found to be maximum at half-filling and superconductivity does not appear for low doping. The maximum value of $T_c$ obtainable for an optimum doping is limited by the structural transition temperature $T_s$. The growth of distortion is arrested with the onset of superconductivity and the distortion is found to disappear at lower temperature for some hole density. Such arresting of the growth of distortion at $T_c$ produces discontinuous jump in thermal expansion coefficient. The variation of strain with temperature as well as with doping, thermal expansion coefficient, the $T_c$ vs $\delta$ behaviour are in qualitative agreement with recent experimental observations on interplay of distortion and superconductivity in cuprates.