Temperature-Induced Superconductivity Enhancement under Large Exchange Field

TL;DR

This paper reveals that in superconductors with large exchange fields, increasing temperature can unexpectedly enhance superconductivity due to the interplay of thermal effects and spin depairing, especially in multiband systems.

Contribution

It introduces a theoretical framework showing temperature-induced superconductivity enhancement under large exchange fields, supported by a two-band model analysis.

Findings

Superconductivity can be enhanced by temperature when Zeeman energy exceeds the order parameter.

Multiband effects can facilitate temperature-induced superconductivity enhancement.

Conditions for observing this phenomenon are identified in materials like MgB2 and FeSe.

Abstract

Through a comprehensive free energy analysis, we demonstrate that finite temperature can simultaneously weaken superconductivity and mitigate spin polarization induced depairing, leading to potential non-monotonic temperature-dependent behaviors in superconductors subjected to large exchange fields. Remarkably, superconductivity can be counterintuitively enhanced by temperature when the Zeeman energy exceeds the superconducting order parameter, owing to the competition between thermal and magnetic effects. We propose that multiband effect offers one possible microscopic route for this temperature-induced enhancement and demonstrate it explicitly within a two-band superconducting model. A detailed parameter analysis identifies the conditions under which this phenomenon emerges, suggesting that temperature-enhanced superconductivity may be observable in materials such as MgB2 and FeSe through transport and tunneling measurements.