Optical properties of layered superconductor LixZrNCl

We investigated band-insulator-to-superconductor transition in Li_xZrNCl driven by carrier doping by means of magnetization, resistivity, and optical reflectivity measurements. The magnetization and the resistivity measurements showed that the transition occurs at around x=0.05. The pristine β-ZrNCl exhibited reflectivity and optical conductivity spectra typical of an insulator, whereas in the spectrum of Li_0.37ZrNCl, Drude-like high reflectance band and associated plasma edge are apparently observed. This is the direct spectroscopic evidence of insulator-to-metal transition of Li_xZrNCl.