Filling control and Mott transitin in 3d transition metal oxides

(1)本文系统地研究了<1-x>不同稀土离子R（=La，Pr，Nd，Sm，Y）对R_Ca_xTiO_3的光学光谱的影响。R_Ca_xTiO_3是一个典型的三维关联电子系统，其电子关联强度（U/W）和能带填充（n）分别随R和Ca浓度X的变化而变化。随着n从1减小，Mott-间隙激发的光谱塌陷并且Drude部分演化。我们发现，当U/W接近带宽控制的Mott跃迁临界值（U/W）_c时，Drude部分随名义空穴掺杂水平delta（=1-n）的演化速率急剧增加。(2)本文研究了掺杂诱导的La_ Sr_xVO_（3 '）的绝缘体-金属（I-M）转变的电磁和光学性质的变化<1-x>，其中LaVO_3是一种3d^2莫特绝缘体。在光谱中，I-M跃迁的特征在于掺杂引起的光谱权重向I的转移。 关于我们 n-能隙区临界磁相界附近金属相的电阻率在很宽的温度范围内（2- 200 K）表现出如下的温度依赖关系：ρ o = ρ o + Δ T_（？<1.5>）(3)RNiO_3具有低自旋态的3d^7构型的Ni^&lt;3+&gt;离子（即，旋转1/2）。与RTiO_（3 '）的情况相似，该体系在室温下的光谱表明，在很宽的能量范围内存在光谱重量转移我们还测量了NdNiO_（3+）在温度变化下的光谱，在200 K下经历了从顺磁金属到反铁磁绝缘体的相变，发现了在200 K以下的电荷能隙的开放以及在0.3eV以上的能量范围内丢失的光谱权重的重新分布。少

(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 … More 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