The optical absorption in indirect semiconductor to semimetal PtSe2 arises from direct transitions

TL;DR

This study clarifies that the optical absorption in PtSe2, transitioning from an indirect semiconductor to a semimetal, is due to direct electronic transitions, enhancing understanding of its electronic phase change.

Contribution

The paper demonstrates through experimental and theoretical analysis that optical absorption in PtSe2 originates solely from direct transitions, challenging previous assumptions about indirect transition contributions.

Findings

Optical absorption in PtSe2 is due to direct transitions.

Transition from semiconductor to semimetal affects optical properties.

Stacking and excitons influence absorption characteristics.

Abstract

$\rm{PtSe_2}$ is a van der Waals material transitioning from an indirect bandgap semiconductor to a semimetal with increasing thickness. Its absorption threshold has been conjectured to originate from interband indirect transitions. By quantitative comparison between broadband ($0.8 - 3.0\,\rm{eV}$) optical absorption of high-quality exfoliated crystals and DFT ab-initio simulations, we prove instead that the optical absorption arises only from direct transitions. This understanding allows us to shed light on the semiconductor to semimetal transition and to explore the effect of stacking and excitons on the optical absorption.