OPTICAL-CONDUCTIVITY SPECTRA OF SR1-XLAXTIO3 - FILLING-DEPENDENT EFFECT OF THE ELECTRON CORRELATION

Optical-conductivity spectra have been measured on the correlated electron system Sr1-xLaxTiO3 (0 less-than-or-equal-to x less-than-or-equal-to 1) in order to determine how the electronic structure depends on the filling of the 3d-electron conduction band. While metallic resistivity was observed in ail samples with x greater-than-or-equal-to 0.1, the optical-conductivity spectra have revealed a critical change in the electronic structure: The effective carrier mass, which has been deduced by analysis of the optical-conductivity spectra and the energy-loss function, is critically enhanced as the x = 1 filling case (Ti 3d1 configuration) is approached, perhaps due to electron-correlation effects, in a manner reminiscent of the Mott-Hubbard transition.