  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 Hc2 at the superconducting transition temperature Tc (i.e.
-dHc2/dT) for FeSe0.7Te0.3 thin films. The in-plane strain tunes Tc in a broad
range, while the composition and disorder are almost unchanged. We show that
-dHc2/dT scales linearly with Tc, indicating that FeSe0.7Te0.3 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.
