Optical properties of the iron-based superconductor LiFeAs single crystal

We have measured the reflectivity spectra of the LiFeAs ( T _c = 17.6 K) single crystal in the temperature range from 4 to 300 K. In the superconducting (SC) state ( T T _c ), the optical conductivity spectra display typical metallic behavior with the Drude-type spectra at low frequencies, but we found that the introduction of the two Drude components best fits the data, indicating the multiband nature of this compound. A theoretical analysis of the low-temperature data ( T = 4 K 200 cm ^−1 ), we have also performed the local-density approximation band calculation and calculated the optical spectra of the interband transitions. This theoretical result provided qualitative agreement with the experimental data below 4000 cm ^−1 .