Orbital Physics in Transition-Metal Oxides

TLDR

In transition‑metal oxides, the orbital shape of d‑electrons and their strong Coulomb interactions drive metal‑insulator transitions, high‑temperature superconductivity, and colossal magnetoresistance, with orbital order or disorder coupling to charge, spin, and lattice dynamics. An overview is provided on orbital physics as a key concept for the science and technology of correlated electrons.

Abstract

An electron in a solid, that is, bound to or nearly localized on the specific atomic site, has three attributes: charge, spin, and orbital. The orbital represents the shape of the electron cloud in solid. In transition-metal oxides with anisotropic-shaped d-orbital electrons, the Coulomb interaction between the electrons (strong electron correlation effect) is of importance for understanding their metal-insulator transitions and properties such as high-temperature superconductivity and colossal magnetoresistance. The orbital degree of freedom occasionally plays an important role in these phenomena, and its correlation and/or order-disorder transition causes a variety of phenomena through strong coupling with charge, spin, and lattice dynamics. An overview is given here on this "orbital physics," which will be a key concept for the science and technology of correlated electrons.