# Superconducting fluctuations in FeSe$_{0.5}$Te$_{0.5}$ thin films probed via microwave spectroscopy

## TL;DR

This study uses microwave spectroscopy to explore superconducting fluctuations in FeSe$_{0.5}$Te$_{0.5}$ thin films, revealing a dimensional crossover and universality class consistent with the 3D-XY model, with fluctuations extending well above Tc.

## Contribution

First to analyze the critical behavior of superconducting fluctuations in FeSe$_{0.5}$Te$_{0.5}$ films using microwave spectroscopy and identify the universality class.

## Key findings

- Superconducting fluctuations extend at least up to 1.1 Tc.
- Dimensional crossover from 2D to 3D observed with increasing film thickness.
- Universality class of the transition is 3D-XY.

## Abstract

We investigated the microwave conductivity spectrum of FeSe$_{0.5}$Te$_{0.5}$ epitaxial films on CaF$_2$ 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 to three-dimensional as the film thickness increased. From the temperature dependence of the scaling parameters we conclude that the universality class of the superconducting transition in FeSe$_{0.5}$Te$_{0.5}$ is that of the 3D-XY model. The lower limit of the onset temperature of the superconducting fluctuations, Tonset, determined by our measurements was 1.1 Tc, suggesting that the superconducting fluctuations of FeSe$_{0.5}$Te$_{0.5}$ are at least as large as those of optimally- and over-doped cuprates.