Coupled charge and spin dynamics in high-density ensembles of nitrogen-vacancy centers in diamond

TL;DR

This study investigates the coupled charge and spin dynamics in dense ensembles of nitrogen-vacancy centers in diamond, revealing how charge state conversions and spin relaxation influence luminescence decay profiles under various conditions, with implications for quantum sensing.

Contribution

It provides new insights into the interplay between charge state dynamics and spin relaxation in high-density NV ensembles, highlighting their impact on luminescence behavior and potential sensing applications.

Findings

Charge dynamics dominate in NV-dense samples even at low excitation power.

Decay profiles vary with NV density and excitation power, showing exponential and inverted exponential behaviors.

Charge state recharging influences the initial luminescence rise and overall spin relaxation processes.

Abstract

We studied the spin depolarization of ensembles of nitrogen-vacancy (NV) centers in nitrogen-rich single crystal diamonds. We found a strong dependence of the evolution of the polarized state in the dark on the concentration of NV centers. At low excitation power, we observed a simple exponential decay profile in the low-density regime and a paradoxical inverted exponential profile in the high-density regime. At higher excitation power, we observed complex behavior, with an initial sharp rise in luminescence signal after the preparation pulse followed by a slower exponential decay. Magnetic field and excitation laser power-dependent measurements suggest that the rapid initial increase of the luminescence signal is related to recharging of the nitrogen-vacancy centers (from neutral to negatively charged) in the dark. The slow relaxing component corresponds to the longitudinal spin relaxation of the NV ensemble. The shape of the decay profile reflects the interplay between two mechanisms: the NV charge state conversion in the dark and the longitudinal spin relaxation. These mechanisms, in turn, are influenced by ionization, recharging and polarization dynamics during excitation. Interestingly, we found that charge dynamics are dominant in NV-dense samples even at very feeble excitation power. These observations may be important for the use of ensembles of NV centers in precession magnetometry and sensing applications.