"Exploratory Materials and Properties of 3d Transition Metal Oxides with Mott Transitions"

本项目的目的是对3d电子跃迁金属氧化物和球晶的Mott相变及其附近的反常金属态进行系统和全面的研究。作为填充控制Mott相变的原型，钙钛矿型钛氧化物通过电子比热、光谱、光电子能谱和核磁共振的测量，揭示了Mott相变附近的量子临界特征，特别是在强质量重整化金属态上。由于巨磁电阻(CMR)效应引起了人们的极大兴趣，钙钛矿型锰氧化物被视为Mott相变的另一个原型。在这个项目中，通过各种实验手段广泛地研究了自旋、电荷和轨道(晶格)动力学之间的相互关系。特别是，本研究首次指出了与轨道动力学有关的反常金属态的存在，电荷有序或伴随的电荷/轨道有序是关联电子的一般特征之一。通过测量中子的散射、输运和光学性质，以及不受限制的Hartree-Fock计算，研究了锰氧化物和镍氧化物的这一现象，以阐明自旋、电荷和轨道扇区之间的相互关系。在这个项目中，许多可能与Mott转变和超导电性有关的自旋能隙系统得到了创新，并通过磁测量(核磁共振和中子散射)进行了广泛的研究。

The aim of this project was to perform systematic and comprehensive study on the Mott transition as well as on the anomalous metallic state near it for 3d electron transition metal oxides and chalogenides.As a prototype of the filling-control Mott transition, the perovskite-type Ti-oxides have been investigated by measurements of electronic specific heat, optical spectra, photoemission spectra, and NMR to reveal the quantum critical features near the Mott transition, in particular on strongly mass-renormalized metallic states.The perovskite-type Mn-oxides, that are attracting great current interest in the light of colossal magnetoresitance (CMR) effect, are viewed as another prototype of the Mott transition system. In this project, the interrelation among the spin, charge, and orbital (lattice) dynamics has been extensively investigated by various experimental means. In particular, the presence of the anomalous metallic state relevant to the orbital dynamics has for the first time been pointed out in the present study.The charge ordering or concomitant charge/orbital ordering is one of generic features for the correlated electron. The phenomena have been investigated for the Mn-oxides and Ni-oxides by measurements of neutron scattering, transport , and optical properties as well as by unrestricted Hartree-Fock calculations to clarify the interrelation among the spin, charge, and orbital sectors.Many spin-gap systems possibly relevant to Mott transition and superconductivity have been innovated in this project and extensively investigated by magentic (NMR and neutron scattering) measurements.