Nonextensive thermodynamics applied to superconductivity

TL;DR

This paper applies nonextensive thermodynamics using Tsallis' entropy to superconductivity, showing that small deviations from standard theory better match experimental data, especially in high-Tc superconductors like YBCO.

Contribution

It introduces a generalized BCS theory with a nonextensivity parameter q, explaining power-law behaviors in superconductors and extending the framework to high-Tc materials.

Findings

q close to 1 describes weak-coupling superconductors

Power-law behavior observed in high-Tc superconductors

Calculated phase diagram and specific heat match experimental data for YBCO

Abstract

We have shown that the weak-coupling limit superconductors are well described by $ q \sim 1 $, where $ q $ is a real parameter which characterizes the degree of nonextensivity of Tsallis' entropy. Nevertheless, small deviations with respect to q=1 provide better agreement when compared with experimental results. We have also shown that the generalized BCS theory with $ q \neq 1 $ exhibit power-law behavior of several measurable macroscopic functions in the low-temperature regime. These power-law properties are found in many high-Tc oxides superconductors and motivated us to extend Tsallis' entropy calculations to these systems. Therefore, we have calculated the phase diagram and the specific heat and we compare our results with the experimental data for the YBCO compound.