Optical properties of the iron-chalcogenide superconductor FeTe0.55Se0.45

TL;DR

This study investigates the optical properties of FeTe0.55Se0.45, revealing a transition from Fermi liquid behavior to superconducting gaps below Tc, with results consistent with BCS theory in the dirty limit.

Contribution

It provides detailed optical measurements of FeTe0.55Se0.45 across the superconducting transition, identifying multiple gap features and scaling behavior.

Findings

Optical response shifts from Fermi liquid to superconducting gaps below Tc.

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

Less than 20% of free carriers condense into the superconducting state.

Abstract

The complex optical properties of the iron-chalcogenide superconductor FeTe0.55Se0.45 with Tc=14K have been examined over a wide frequency range for light polarized in the Fe-Te(Se) planes above and below Tc. At room temperature the optical response may be described by a weakly-interacting Fermi liquid; however, just above Tc this picture breaks down and the scattering rate takes on a linear frequency dependence. Below Tc there is evidence for two gap features in the optical conductivity at Delta_1 ~ 2.5 meV and Delta_2 ~ 5.1 meV. Less than 20% of the free carriers collapse into the condensate for T << Tc, and this material is observed to fall on the universal scaling line for a BCS dirty-limit superconductor in the weak-coupling limit.