Enhanced superconducting-fluctuation effects on thermodynamic properties in BCS-BEC-crossover regime

TL;DR

This paper investigates how strong superconducting fluctuations in the BCS-BEC crossover regime significantly alter thermodynamic properties, leading to enhanced fluctuation effects and potential explanations for anomalous diamagnetic responses.

Contribution

It reveals the crucial role of mode coupling in superconducting fluctuations near the BCS-BEC crossover, affecting critical temperatures and thermodynamic responses.

Findings

Superconducting fluctuations are strongly enhanced near the BCS-BEC crossover.

Mode coupling between fluctuations lowers the critical temperature and depairing field.

Enhanced fluctuations can explain anomalous diamagnetic responses in FeSe.

Abstract

Effects of superconducting fluctuation (SCF) on thermodynamic properties of electron systems in the so-called BCS-BEC-crossover regime are studied. As the attractive interaction between electrons becomes stronger upon approaching the BCS-BEC-crossover regime, importance of the mode coupling between SCF drastically increases. The enhanced mode coupling leads to lowering of both the zero-field superconducting critical temperature and the depairing field $B_\text{c2} (T)$. Consequently, SCF-induced contributions to the specific heat and the diamagnetic susceptibility can seemingly exceed the corresponding values in the Gaussian approximation. We discuss relevance of the present results to the anomalous SCF-induced diamagnetic response observed in the iron selenide (FeSe).