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

Abstract

The superconducting order parameter in the iron-chalcogenide superconductor FeTe${}_{0.55}$Se${}_{0.45}$ ($T_{\text{c}}$ = 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 $T_{\text{c}}$ to $\sim 18-20$ K and possible origins, including novel quasiparticle scattering due to strong antiferromagnetic spin fluctuations, are discussed.

5 pages, 3 figures

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