Temperature-dependent optical constants of nanometer-thin flakes of Fe(Te,Se) superconductor in the visible and near-infrared regime

Iron chalcogenide superconductors, such as Fe(Te,Se), have recently garnered significant attention due to their simple crystal structure with a relatively easy synthesis process, high-temperature superconductivity, intrinsic topological band structure, and an unconventional pairing of superconductivity with ferromagnetism. Here, we report the complex in-plane refractive index measurement of a nanometer-thin Fe(Te,Se) flake exfoliated from a single crystal FeTe0.6Se0.4 for photon wavelengths from 450 to 1100 nm over a temperature range from 4 to 295 K. The results were obtained by employing a two-Drude model for the dielectric function of Fe(Te,Se), a multiband superconductor, and fitting the absolute optical reflection spectra using the transfer matrix method. A high extinction coefficient in the visible to near-infrared range makes nanometer-thin Fe(Te,Se) flakes a promising material for photodetection applications.