Spin Coherence and $^{14}$N ESEEM Effects of Nitrogen-Vacancy Centers in Diamond with X-band Pulsed ESR

TL;DR

This study reports pulsed ESR experiments on nitrogen-vacancy centers in diamond, demonstrating long coherence times after proper annealing, and characterizing hyperfine interactions with nitrogen and carbon nuclei using ESEEM spectroscopy.

Contribution

It provides detailed analysis of spin coherence and nuclear interactions in NV centers at X-band, highlighting the importance of annealing for optimizing coherence times.

Findings

Achieved spin coherence times of 0.74 ms at 5 K.

Resolved ESEEM effects from $^{14}$N and $^{13}$C nuclei.

Determined hyperfine and quadrupole tensors for $^{14}$N.

Abstract

Pulsed ESR experiments are reported for ensembles of negatively-charged nitrogen-vacancy centers (NV$^-$) in diamonds at X-band magnetic fields (280-400 mT) and low temperatures (2-70 K). The NV$^-$ centers in synthetic type IIb diamonds (nitrogen impurity concentration $<1$~ppm) are prepared with bulk concentrations of $2\cdot 10^{13}$ cm$^{-3}$ to $4\cdot 10^{14}$ cm$^{-3}$ by high-energy electron irradiation and subsequent annealing. We find that a proper post-radiation anneal (1000$^\circ$C for 60 mins) is critically important to repair the radiation damage and to recover long electron spin coherence times for NV$^-$s. After the annealing, spin coherence times of T$_2 = 0.74$~ms at 5~K are achieved, being only limited by $^{13}$C nuclear spectral diffusion in natural abundance diamonds. At X-band magnetic fields, strong electron spin echo envelope modulation (ESEEM) is observed originating from the central $^{14}$N nucleus. The ESEEM spectral analysis allows for accurate determination of the $^{14}$N nuclear hypefine and quadrupole tensors. In addition, the ESEEM effects from two proximal $^{13}$C sites (second-nearest neighbor and fourth-nearest neighbor) are resolved and the respective $^{13}$C hyperfine coupling constants are extracted.