Level anti-crossing spectra of nitrogen-vacancy centers in diamond detected by using modulation of the external magnetic field

TL;DR

This study investigates the magnetic field dependence of NV- centers in diamond, revealing how modulation frequency affects level anti-crossing signals and providing a theoretical model to optimize detection sensitivity.

Contribution

The paper introduces a theoretical model explaining the effects of magnetic field modulation on LAC signals in NV centers, enhancing the understanding of spin dynamics and detection optimization.

Findings

LAC line amplitudes increase significantly at lower modulation frequencies.

Good agreement between experimental data and the theoretical model.

Coherent spin polarization exchange drives the observed effects.

Abstract

We report a study of the magnetic field dependence of the photo-luminescence of NV$^-$ centers (negatively charged nitrogen-vacancy centers) in diamond single crystals. In such a magnetic field dependence characteristic lines are observed, which are coming from Level Anti-Crossings (LACs) in the coupled electron-nuclear spin system. For enhancing the sensitivity, we used lock-in detection to measure the photo-luminescence intensity and observed a remarkably strong dependence of the LAC-derived lines on the modulation frequency. Upon decreasing of the modulation frequency from 12 kHz to 17 Hz the amplitude of the lines increases by approximately two orders of magnitude. To take a quantitative account for such effects, we developed a theoretical model, which describes the spin dynamics in the coupled electron-nuclear spin system under the action of an oscillating external magnetic field. Good agreement between experiments and theory allows us to conclude that the observed effects are originating from coherent spin polarization exchange in the NV$^-$ center. Our results are of great practical importance allowing one to optimize the experimental conditions for probing LAC-derived lines in diamond defect centers.