Universal scaling behavior of the upper critical field in strained FeSe0.7Te0.3 thin films

Abstract

Revealing the universal behaviors of iron-based superconductors (FBS) is important to elucidate the microscopic theory of superconductivity. In this work, we investigate the effect of in-plane strain on the slope of the upper critical field H _c2 at the superconducting transition temperature T _c (i.e. −d H _c2 /d T ) for FeSe _0.7 Te _0.3 thin films. The in-plane strain tunes T _c in a broad range, while the composition and disorder are almost unchanged. We show that −d H _c2 /d T scales linearly with T _c , indicating that FeSe _0.7 Te _0.3 follows the same universal behavior as observed for pnictide FBS. The observed behavior is consistent with a multiband superconductivity paired by interband interaction such as sign change s _± superconductivity.

Keywords

• Fe-based superconductors
• thin film
• upper critical fields