|Budget Amount *help
¥7,300,000 (Direct Cost : ¥7,300,000)
Fiscal Year 1995 : ¥2,300,000 (Direct Cost : ¥2,300,000)
Fiscal Year 1994 : ¥5,000,000 (Direct Cost : ¥5,000,000)
(1) Optical spectra have been systematically investigated for R_<1-x>Ca_xTiO_3 with various rare earth ions R (=La, Pr, Nd, Sm, and Y) as a typical three-dimensional correlated electron system , in which both the electron-correlation strength (U/W) and the band filling (n) can be varied by means of changes of R and Ca concentrasion X,respectively. With a decrease of n from 1, the spectrum of the Mott-gap excitation collapses and the Drude part evolves. We found that the rate of the Drude-part evolution with the nominal hole-doping level delta (=1-n) is critically enhanced as U/W approaches the critical value (U/W)_c for the band width-control Mott transition.
(2) Changes in electrical magnetic, and optical properties have been investigated for the doping-induced insulator-metal (I-M) transition in La_<1-x>Sr_xVO_<3'> where the end compound LaVO_3 is a 3d^2 Mott insulator. In the optical spectra, the I-M transition is characterized by doping-induced transfer of spectral weight into the i
n-gap region. Resistivity in the metallic phase near the critical magnetic phase boundary shows such a temperature dependence as expressed by the relation rho=rho+AT^<1.5> over a wide temperature range (2-200K) with the enhanced coefficient A towards the phase boundary Such resultsccan be explained in terms of the effect of the antiferromagnetic spin fluctuation on the charge transport.
(3) RNiO_3 has the Ni^<3+> ion in the 3d^7configuration with low-spin state (i.e., spin 1/2). and shows metallic or insulating behavior depending on the ionic rarius of the R,as is similar to the case of RTiO_<3'> We investigated optical spectra of this system at room temperature, and found spectral weight transfer over a wide energy range (up to several eV) with the changes of R.We also measured the optical spectrum under variation of temperature for NdNiO_<3, > which undergoes a phase transition from a paramagnetic metal to an antiferromagnetic insulator at 200K,and found the opening of a charge gap below 200K as well as the redistribution of the missing spectral weight over the energy range above 0.3 eV. Less