Doping Variation of Optical Properties in ZrNCl Superconductors

Abstract

Systematic optical reflectivity measurements were performed on a series of electron-doped layered nitride Li x ZrNCl superconductors with a variable carrier density. A Drude band grew up with increasing Li doping level x , providing optical evidence of a transition from a band insulator to a metal. The doping variation of the plasma edge exhibited excellent agreement with the results of first-principles calculations. Furthermore, the good agreement among the optical, thermal, and theoretical effective masses highlights the uniqueness of the present materials, indicating that relatively high T c superconductivity with T c ∼15 K can emerge from a light effective mass m * ∼0.9 m 0 with minimal renormalization.