Electronic correlations and unusual superconducting response in the optical properties of the iron-chalcogenide FeTe0.55Se0.45

TL;DR

This study investigates the optical properties of FeTe0.55Se0.45, revealing increased electronic correlations at low temperatures and identifying two superconducting gaps, contributing to understanding unconventional superconductivity in iron chalcogenides.

Contribution

It provides detailed optical measurements across the superconducting transition, highlighting the correlation effects and gap features in FeTe0.55Se0.45.

Findings

Conductivity becomes frequency-dependent below 100 K, indicating increased correlations.

Superfluid density and dc conductivity suggest proximity to BCS dirty-limit scaling.

Two superconducting gaps are observed at approximately 2.5 and 5.1 meV.

Abstract

The in-plane complex optical properties of the iron-chalcogenide superconductor FeTe0.55Se0.45 have been determined above and below the critical temperature Tc = 14 K. At room temperature the conductivity is described by a weakly-interacting Fermi liquid; however, below 100 K the scattering rate develops a frequency dependence in the terahertz region, signaling the increasingly correlated nature of this material. We estimate the dc conductivity just above Tc to be sigma_dc ~ 3500 Ohm-1cm-1 and the superfluid density rho_s0 ~ 9 x 10^6 cm-2, which places this material close to the scaling line rho_s0/8 ~ 8.1 sigma_dc Tc for a BCS dirty-limit superconductor. Below Tc the optical conductivity reveals two gap features at Delta_1,2 ~ 2.5 and ~ 5.1 meV.