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

The complex optical properties of the iron-chalcogenide superconductor FeTe0.55Se0.45 with T c=14 K have been examined over a wide frequency range for light polarized in the Fe–Te(Se) planes above and below T c. At room temperature the optical response may be described by a weakly interacting Fermi liquid; however, just above T c this picture breaks down and the scattering rate takes on a linear frequency dependence. Below T c there is evidence for two gap features in the optical conductivity at View the MathML sourceΔ1≃2.5meV and View the MathML sourceΔ2≃5.1meV. Less than 20% of the free carriers collapse into the condensate for T⪡TcT⪡Tc, and this material is observed to fall on the universal scaling line for a BCS dirty-limit superconductor in the weak-coupling limit.