Electronic correlations and unusual superconducting response in the optical properties of the iron-chalcogenide FeTe0.55Se0.45
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 sigmadc ~ 3500 Ohm-1cm-1 and the superfluid density rhos0 ~ 9 x 106 cm-2, which places this material close to the scaling line rhos0/8 ~ 8.1 sigmadc Tc for a BCS dirty-limit superconductor. Below Tc the optical conductivity reveals two gap features at Delta1,2 ~ 2.5 and ~ 5.1 meV.