Superconducting fluctuations in FeSe0.5Te0.5 thin films probed via microwave spectroscopy

We investigated the microwave conductivity spectrum of FeSe0.5Te0.5 epitaxial films on CaF2 in the vicinity of the superconducting transition. We observed the critical behavior of the superconducting fluctuations in these films with a dimensional crossover from two dimensional (2D) to three dimensional (3D) as the film thickness increased. From the temperature dependence of the scaling parameters we conclude that the universality class of the superconducting transition in FeSe0.5Te0.5 is that of the 3D-XY model. The lower limit of the onset temperature of the superconducting fluctuations Tonset determined by our measurements was 1.1Tc, suggesting that the superconducting fluctuations of FeSe0.5Te0.5 are at least as large as those of optimally and overdoped cuprates.