Brightening interlayer excitons by electric-field-driven hole transfer in bilayer WSe2

TL;DR

This study demonstrates that electric fields can induce interlayer hole transfer in bilayer WSe2, making interlayer excitons optically bright by imparting intralayer character, which is confirmed by experiments and DFT calculations.

Contribution

It reveals a novel mechanism where electric-field-driven hole transfer enhances interlayer exciton brightness without requiring hybridization.

Findings

Interlayer excitons remain bright under electric fields in bilayer WSe2.

DFT calculations show electric fields distort valence-band states, causing hole transfer.

Simulations confirm hole transfer as the main reason for brightening, not hybridization.

Abstract

We observe the interlayer A1s^I, A2s^I, and B1s^I excitons in bilayer WSe2 under applied electric fields using reflectance contrast spectroscopy. Remarkably, these interlayer excitons remain optically bright despite being well separated from symmetry-matched intralayer excitons-a regime where conventional two-level coupling models fail unless unphysically large coupling strengths are assumed. To uncover the origin of this brightening, we perform density functional theory (DFT) calculations and find that the applied electric field distorts the valence-band Bloch states, driving the hole wavefunction from one layer to the other. This field-driven interlayer hole transfer imparts intralayer character to the interlayer excitons, thereby enhancing their oscillator strength without requiring hybridization with bright intralayer states. Simulations confirm that this mechanism accounts for the major contribution to the observed brightness, with excitonic hybridization playing only a minor role. Our results identify interlayer hole transfer as a robust and general mechanism for brightening interlayer excitons in bilayer transition metal dichalcogenides (TMDs), especially when inter- and intralayer excitons are energetically well separated.