Review—Orbital Physics: Glorious Past, Bright Future

Abstract

Transition metal (TM) compounds present a very big class of materials with quite diverse properties. There are insulators, metals and systems with insulator–metal transitions among them; most magnetic systems are TM compounds; there are also (high- T c ) superconductors among them. Their very rich properties are largely determined by the strong interplay of different degrees of freedom: charge; spin; orbital; lattice. Orbital effects play a very important role in these systems—and not only in them! The study of this field, initiated by Goodenough almost 70 years ago, turned out to be very fruitful and produced a lot of important results. In this short review I discuss the basics of orbital physics and summarize the main achievements in this big field, in which Goodenough played a pivotal role, and which are nowadays widely used to explain many properties of TM compounds. In the main part of the text I discuss novel developments and perspectives in orbital physics, which is still a very active field of research, constantly producing new surprises.