Strong Coupling Superconductivity in Iron-Chalcogenide FeTe$_{0.55}$Se$_{0.45}$

TL;DR

This study investigates the superconducting properties of FeTe$_{0.55}$Se$_{0.45}$, revealing strong-coupling superconductivity with an s-wave symmetry and a persistent conductance enhancement above the critical temperature, possibly due to spin fluctuations.

Contribution

First detailed point-contact spectroscopy analysis showing strong-coupling s-wave superconductivity in FeTe$_{0.55}$Se$_{0.45}$ with no evidence of multiple gaps.

Findings

Energy gap of 3.8 meV at 1.70 K

Strong-coupling superconductivity confirmed

Conductance enhancement persists above $T_c$

Abstract

The superconducting order parameter in the iron-chalcogenide superconductor FeTe$_{0.55}$Se$_{0.45}$ ($T_\textrm{c}$ = 14.2 K) is investigated by point-contact Andreev reflection spectroscopy. The energy gap magnitude (3.8 meV at 1.70 K) and temperature dependence as extracted from the Andreev conductance spectra reveal strong-coupling superconductivity and is consistent with $s$-wave order parameter symmetry. No clear evidence for multiple order parameters or interference from multiple bands is observed. A conductance enhancement persists above $T_\textrm{c}$ to $\sim 18-20$ K and possible origins, including novel quasiparticle scattering due to strong antiferromagnetic spin fluctuations, are discussed.