Optically-active spin defects in hexagonal boron nitride (hBN) are promising quantum systems for the design of two-dimensional quantum sensing units offering optimal proximity to the sample being probed. In this work, we first demonstrate that the electron spin resonance frequencies of boron vacancy centres (VB−) can be detected optically in the limit of few-atomic-layer thick hBN flakes despite the nanoscale proximity of the crystal surface that often leads to a degradation of the stability of solid-state spin defects. We then analyze the variations of the electronic spin properties of VB− centres with the hBN thickness with a focus on (i) the zero-field splitting parameters, (ii) the optically-induced spin polarization rate and (iii) the longitudinal spin relaxation time. This work provides important insights into the properties of VB− centres embedded in ultrathin hBN flakes, which are valuable for future developments of foil-based quantum sensing technologies.
@article{arxiv.2304.12071,
title = {Optically-active spin defects in few-layer thick hexagonal boron nitride},
author = {A. Durand and T. Clua-Provost and F. Fabre and P. Kumar and J. Li and J. H. Edgar and P. Udvarhelyi and A. Gali and X. Marie and C. Robert and J. M. Gérard and B. Gil and G. Cassabois and V. Jacques},
journal= {arXiv preprint arXiv:2304.12071},
year = {2023}
}