Dimensionality of excitons in stacked van der Waals materials: The example of hexagonal boron nitride

TL;DR

This paper investigates how layer stacking in hexagonal boron nitride influences the dimensionality and nature of electron-hole pairs, revealing four types of excitons with varying spatial and optical properties.

Contribution

It provides a detailed analysis of exciton types in van der Waals materials based on stacking, offering insights for predicting and tailoring excitonic properties.

Findings

Four types of excitons identified with different dimensionalities

Electron-hole distributions can be overlapping or charge-transfer

Structural and symmetry conditions determine exciton properties

Abstract

With the example of hexagonal boron nitride, we demonstrate how the character of electron-hole (e-h) pairs in van der Waals bound low-dimensional systems is driven by layer stacking. Four types of excitons appear, with either a two- or three-dimensional spatial extension. Electron and hole distributions are either overlapping or exhibit a charge-transfer nature. We discuss under which structural and symmetry conditions they appear and they are either dark or bright. This analysis provides the key elements to identify, predict, and possibly tailor the character of e-h pairs in van der Waals materials.