Optical reflectivity spectra measured on cleaved surfaces of Nd0.5Sr0.5MnO3

Optical reflectivity study of Nd0.5Sr0.5MnO3 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 (less than or equal to0.1. 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.