Temperature-dependent optical spectroscopy studies of Nd1−xTiO3

The temperature dependent optical spectra are investigated in a well-characterized titanate system, Nd1−xTiO3, between 50 and 40 000cm−1 at three different doping levels, x=0.019, 0.046, and 0.095, corresponding to a Mott-Hubbard insulator, a semiconductor and a correlated metal, respectively. Mid-gap states develop inside the Hubbard gap with hole doping. Based on the room-temperature spectra of the optical conductivity, the evolution rate of …