Valley excitons in two-dimensional semiconductors

TL;DR

This paper reviews the unique properties of valley excitons in monolayer transition metal dichalcogenides, highlighting their strong Coulomb interactions, valley-dependent optical selection rules, and potential for novel optoelectronic applications.

Contribution

It provides a comprehensive overview of recent experimental and theoretical advances in understanding valley excitons in two-dimensional semiconductors.

Findings

Valley excitons exhibit strong Coulomb binding.

Valley-dependent optical selection rules enable valley-specific control.

Unique excitonic features arise from two-dimensional geometry and valley degeneracy.

Abstract

Monolayer group-VIB transition metal dichalcogenides have recently emerged as a new class of semiconductors in the two-dimensional limit. The attractive properties include: the visible range direct band gap ideal for exploring optoelectronic applications; the intriguing physics associated with spin and valley pseudospin of carriers which implies potentials for novel electronics based on these internal degrees of freedom; the exceptionally strong Coulomb interaction due to the two-dimensional geometry and the large effective masses. The physics of excitons, the bound states of electrons and holes, has been one of the most actively studied topics on these two-dimensional semiconductors, where the excitons exhibit remarkably new features due to the strong Coulomb binding, the valley degeneracy of the band edges, and the valley dependent optical selection rules for interband transitions. Here we give a brief overview of the experimental and theoretical findings on excitons in two-dimensional transition metal dichalcogenides, with focus on the novel properties associated with their valley degrees of freedom.