Optical Reflectivity Spectra Measured on Cleaved Surfaces of Nd_0.5Sr_0.5MnO₃

Abstract

Optical reflectivity study of Nd_0.5Sr_0.5MnO₃ using cleaved surfaces demonstrates that the optical spectra are susceptible to the surface deterioration for the ferromagnetic-metallic as well as the charge-ordered phases. The charge gap estimated from the spectrum obtained on the polished surface (≤0.1 eV) is much smaller than that estimated from the spectrum obtained on the cleaved surface (>0.5 eV). The CE-type charge-ordered state can be easily damaged by disorder. The optical conductivity in the metallic phase exhibits a mid-infrared structure in addition to the metallic Drude peak. This indicates that short-range charge ordering persists even in the metallic phase.