Orbital physics: glorious past, bright future

TL;DR

This paper reviews the history, current state, and future directions of orbital physics in transition metal compounds, highlighting its importance in understanding diverse material properties and recent advancements.

Contribution

It provides a comprehensive overview of orbital physics, summarizing key achievements and discussing new developments and future perspectives in the field.

Findings

Orbital effects are crucial in determining properties of TM compounds.

Recent research continues to reveal new phenomena in orbital physics.

Orbital physics remains a highly active and evolving research area.

Abstract

Transition metal (TM) compounds present a very big class of materials with quite diverse properties. There are among them insulators, metals, systems with insulator-metal transitions; most magnetic systems are TM compounds; there are among them also (high-Tc) superconductors. 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 first discuss the basics of orbital physics, 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.