Interacting donor-acceptor pairs as the origin of coupled spin-optical signals in hexagonal boron nitride

TL;DR

This study reveals that coupled donor-acceptor defect pairs in hexagonal boron nitride are responsible for spin-optical signals, providing a microscopic understanding crucial for quantum technology applications.

Contribution

The paper introduces a first-principles framework showing coupled defect pairs, not isolated defects, as the origin of spin-optical signals in hexagonal boron nitride.

Findings

Coupled donor-acceptor pairs modulate optical and spin properties.

Identification of two charge-state-dependent coupling regimes.

Extension of the model to defect ensembles explains experimental diversity.

Abstract

Optically addressable spin defects in hexagonal boron nitride hold promise for room-temperature quantum technologies, but their microscopic identities remain largely unknown. Using first principles calculations, we show that coupled spin optical signals arise from interacting donor acceptor pairs, not the commonly believed isolated defects. Intra and inter pair separations control charge transfer, electronic structure, and spin coupling, thereby greatly modulating zero phonon lines, phonon sidebands, lifetimes, and the sign of optically detected magnetic resonance contrast. Importantly, we identify two distinct charge-state-dependent coupling regimes and extend this picture to correlated defect ensembles, explaining the wide diversity of experimental observations. Our results establish a microscopic framework for coupled defect behavior and provide design principles for spin-active quantum emitters in wide bandgap semiconductors.