Towards $\textit{ab initio}$ identification of paramagnetic substitutional carbon defects in hexagonal boron nitride acting as quantum bits

TL;DR

This paper uses ab initio density functional theory to identify and analyze paramagnetic substitutional carbon defects in hexagonal boron nitride as potential quantum bits, correlating theoretical predictions with experimental spectra.

Contribution

It provides the first comprehensive ab initio analysis of C$_ ext{B}$ and C$_ ext{N}$ defects in hBN, linking theoretical charge transition levels to experimental quantum bit signatures.

Findings

Charge transition levels are within the band gap, making them experimentally accessible.

A neutral C$_ ext{B}$ defect matches observed single spin center spectra.

Insights into defect separation effects on electronic properties.

Abstract

Paramagnetic substitutional carbon (C$_\text{B}$, C$_\text{N}$) defects in hexagonal boron nitride (hBN) are discussed as candidates for quantum bits. Their identification and suitability are approached by means of photoluminescence (PL), charge transitions, electron paramagnetic resonance, and optically detected magnetic resonance (ODMR) spectra. Several clear trends in these are revealed by means of an efficient plane wave periodic supercell \textit{ab initio} density functional theory approach. In particular, this yields insight into the role of the separation between C$_\text{B}$ and C$_\text{N}$. In most of the cases the charge transition between the neutral and a singly charged ground state of a defect is predicted to be experimentally accessible, since the charge transition level (CTL) position lies within the band gap. \textit{A posteriori} charge corrections are also discussed. A near-identification of an experimentally isolated single spin center as the neutral C$_\text{B}$ point defect was found via comparison of results to recently observed PL and ODMR spectra.