Singlet levels of the NV$^{-}$ centre in diamond

TL;DR

This paper investigates the singlet states of the NV- centre in diamond, focusing on the infrared transition at 1042 nm, and reveals the underlying electronic interactions and vibronic effects through stress experiments.

Contribution

It provides detailed analysis of the infrared singlet transition in NV- centres, identifying the interactions responsible and confirming the ordering of singlet states.

Findings

Infrared transition shift due to electron-electron Coulomb interaction.

Identification of vibronic level 115 cm^{-1} above the ${}^1E$ state.

Confirmation that ${}^1A_1$ is the upper singlet level.

Abstract

The characteristic transition of the NV- centre at 637 nm is between ${}^3\mathrm{A}_2$ and ${}^3\mathrm{E}$ triplet states. There are also intermediate ${}^1\mathrm{A}_1$ and ${}^1\mathrm{E}$ singlet states, and the infrared transition at 1042 nm between these singlets is studied here using uniaxial stress. The stress shift and splitting parameters are determined, and the physical interaction giving rise to the parameters is considered within the accepted electronic model of the centre. It is established that this interaction for the infrared transition is due to a modification of electron-electron Coulomb repulsion interaction. This is in contrast to the visible 637 nm transition where shifts and splittings arise from modification to the one-electron Coulomb interaction. It is also established that a dynamic Jahn-Teller interaction is associated with the singlet ${}^1\mathrm{E}$ state, which gives rise to a vibronic level 115 $\mathrm{cm}^{-1}$ above the ${}^1\mathrm{E}$ electronic state. Arguments associated with this level are used to provide experimental confirmation that the ${}^1\mathrm{A}_1$ is the upper singlet level and ${}^1\mathrm{E}$ is the lower singlet level.