Introduction

Abstract

One striking point of the Mott insulator is that drastic electronic state change emerges associated with the insulator-metal (Mott) transition. In the vicinity of the Mott transition, a wide variety of phenomena such as high-temperature superconductivity, colossal magnetoresistance, and large thermoelectric effect arises from interplay among charge, spin, and orbital degrees of freedom. While their functional effects should form the significant basis of future oxide electronics, the detailed mechanisms are still under debate. In this thesis, we focus on a couple of transition-metal oxides considered as key materials to solve the pending problems, and investigate their charge dynamics and Mott transition features via spectroscopy. In this Chapter, we briefly overview the theoretical formalisms of the Mott transition, materials systematics ranging over a set of the 3d transition-metal oxides, charge-spin-orbital degrees of freedom, and some fundamental and important features of the charge dynamics observed near the Mott transition.