Sensitive detection of level anticrossing spectra of nitrogen vacancy centers in diamond

Abstract

We report a study of the magnetic field dependence of photoluminescence of NV − centers (negatively charged nitrogen-vacancy centers) in diamond single crystals. In such a magnetic field dependence characteristic sharp features are observed, which are coming from Level Anti-Crossings (LACs) in a coupled electron-nuclear spin system. For sensitive detection of such LAC-lines we use lock-in detection to measure the photoluminescence intensity. This experimental technique allows us to obtain new LAC lines. Additionally, a remarkably strong dependence of the LAC-lines on the modulation frequency is found. Specifically, upon decrease of the modulation frequency from 12 kHz to 17 Hz the amplitude of the LAC-lines increases by approximately two orders of magnitude. To take a quantitative account for such effects, we present a theoretical model, which describes the spin dynamics in a 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 a coupled spin system comprising the spin-polarized NV − center. Our results are of great practical importance allowing one to optimize the experimental conditions for probing LAC-derived lines in diamond crystals comprising NV − centers and for indirect detection and identification of other paramagnetic defect centers.

A method for simulating level anti-crossing spectra of diamond crystals containing NV− color centers

“…Specifically, for weak LAC lines the increase in amplitude upon decreasing the modulation frequency from 12.5 kHz to 17 Hz is an order of magnitude stronger than for intense lines, e.g., than for the LAC line at 1024 G. Thus, the amplitude ratio calculated by using our method is more similar to experimental observations at the modulation frequency of 12.5 kHz, rather than to those at 17 Hz. Numerical calculations [34] show that such an enhancement of LAC lines is due to the fact that nuclear spins, which relax much slower than the electron spins, can store spin polarization. After many excitation-radiation cycles (or excitation-radiationless relaxation), the polarization is transferred from NV − centers to nuclei.…”

“…This is true for the pair NV − /P1 and even to a greater extent for the pair NV − /NV − . Most likely, this discrepancy is caused by the effect of field modulation on LAC lines [34]: at low frequencies the line amplitude strongly increases, this effect is much more pronounced for weak low-amplitude lines.…”

“…Since such defect centers are often "dark" centers, information about such interactions can be deduced indirectly from Level Anti-Crossng (LAC) spectra. Experimentally such LAC spectra of diamond single crystals containing NV − centers can be studied by monitoring the magnetic field dependence of the photoluminescence intensity, which contains sharp features associated with LACs [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. To probe such "LAC lines" no resonant microwave or radiofrequency pumping is required.…”

Optically detected flip-flops between different spin ensembles in diamond

“…MW loop antenna is connected directly to a synthesizer, 100% amplitude modulated by a 151 Hz sine wave. The PD signal is demodulated by a lock-in amplifier [40], and the resulting amplitude is recorded. In all the two dimensional scans the magnetic field is scanned first, slowly enough to avoid hysteresis.…”

Battery characterization via eddy-current imaging with nitrogen-vacancy centers in diamond

“…The PL of a diamond sample displays various cross relaxation features, extensively discussed in the literature [13][14][15], as a function of the bias magnetic field, as shown in Fig. 2.…”