Physics of Excitonic Insulators―Orders and Collective Excitations Derived from Interband Interactions

Abstract

In this article, we present a brief review of the physics of excitonic insulators described as an ordered state of electron and hole pairs. First, we review the theoretical background of the excitonic insulator. Then, we introduce candidate materials for the excitonic insulator that are addressed by recent experiments. Finally, we discuss the collective modes of the excitonic order coupled to phonons and their optical properties.