Exciton spectroscopy of hexagonal boron nitride using non-resonant x-ray Raman scattering

TL;DR

This study uses non-resonant x-ray Raman scattering to analyze exciton properties in hexagonal boron nitride, revealing a dominant Y_{10}-type Frenkel exciton through multiple theoretical approaches.

Contribution

It provides a detailed characterization of excitons in hexagonal boron nitride using combined experimental and theoretical methods, identifying the exciton symmetry and nature.

Findings

Identification of a strong pre-edge feature as a Y_{10}-type Frenkel exciton

Confirmation of exciton symmetry through multiple scattering calculations

Support from Bethe-Salpeter equation calculations

Abstract

We report non-resonant x-ray Raman scattering (XRS) measurements from hexagonal boron nitride for transferred momentum from 2 to 9 $\mathrm{\AA}^{-1}$ along directions both in and out of the basal plane. A symmetry-based argument, together with real-space full multiple scattering calculations of the projected density of states in the spherical harmonics basis, reveals that a strong pre-edge feature is a dominantly $Y_{10}$-type Frenkel exciton with no other \textit{s}-, \textit{p}-, or \textit{d}- components. This conclusion is supported by a second, independent calculation of the \textbf{q}-dependent XRS cross-section based on the Bethe-Salpeter equation.