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

Revealing the universal behaviors of iron-based superconductors (FBS) is\nimportant to elucidate the microscopic theory of superconductivity. In this\nwork, we investigate the effect of in-plane strain on the slope of the upper\ncritical field Hc2 at the superconducting transition temperature Tc (i.e.\n-dHc2/dT) for FeSe0.7Te0.3 thin films. The in-plane strain tunes Tc in a broad\nrange, while the composition and disorder are almost unchanged. We show that\n-dHc2/dT scales linearly with Tc, indicating that FeSe0.7Te0.3 follows the same\nuniversal behavior as observed for pnictide FBS. The observed behavior is\nconsistent with a multiband superconductivity paired by interband interaction\nsuch as sign change s+- superconductivity.\n