Terahertz spectroscopy of superconducting Fe(Se,Te)

Among the iron-based superconductors, Fe(Se,Te) has received special attention due to its simple crystal structure, which is formed by Fe(Se,Te) layers only. Studies of the optical conductivity at terahertz and far-infrared frequencies may bring information about the superconducting energy gap size and symmetry. Here, we present a terahertz investigation of superconducting Fe(Se,Te) thin films at temperatures from 2 to 300 K. The measurements have been performed with a backward-wave-oscillator spectrometer, which allows phase-sensitive measurements of transmission at terahertz frequencies. Thus, both components of the complex dynamical conductivity can be directly obtained from these measurements. In this talk, we discuss the frequency and temperature dependence of complex conductivity in Fe(Se,Te).