Photoionization of negatively charged NV centers in diamond: theory and ab initio calculations

TL;DR

This paper uses ab initio calculations to analyze the photoionization processes of negatively charged NV centers in diamond, explaining charge-state dynamics and spin polarization effects relevant for quantum applications.

Contribution

It provides the first detailed ab initio analysis of NV center photoionization thresholds, cross sections, and spin polarization mechanisms, enhancing understanding of charge-state control.

Findings

Photoionization thresholds and cross sections are calculated accurately.

Ionization from the excited state leads to a metastable neutral state.

Spin polarization of NV- influences the resulting neutral state's spin properties.

Abstract

We present ab-initio calculations of photoionization thresholds and cross sections of the negatively charged nitrogen-vacancy (NV) center in diamond from the ground $^{3}\!A_2$ and the excited $^{3}\!E$ states. We show that after the ionization from the $^{3}\!E$ level the NV center transitions into the metastable $^{4}\!A_2$ electronic state of the neutral defect. We reveal how spin polarization of $\mathrm{NV}^{-}$ gives rise to spin polarization of the $^{4}\!A_2$ state, providing an explanation of electron spin resonance experiments. We obtain smooth photoionization cross sections by employing dense $k$-point meshes for the Brillouin zone integration together with the band unfolding technique to rectify the distortions of the band structure induced by artificial periodicity of the supercell approach. Our calculations provide a comprehensive picture of photoionization mechanisms of $\mathrm{NV}^{-}$. They will be useful in interpreting and designing experiments on charge-state dynamics at NV centers. In particular, we offer a consistent explanation of recent results of spin-to-charge conversion of NV centers.