Detecting External Electron Spins Using Nitrogen-Vacancy Centers

TL;DR

This paper demonstrates the detection of external electron spins using near-surface nitrogen-vacancy centers in diamond, employing double resonance techniques to verify surface spins and develop a model for their magnetic field fluctuations.

Contribution

It introduces a method to detect and analyze external electron spins at the diamond surface using NV centers and double resonance, with a new model for magnetic field fluctuations.

Findings

Detection of surface electron spins confirmed by surface treatments.

Correlation between spin signal size and NV center relaxation time T2.

Active double resonance enhances sensitivity over passive detection.

Abstract

Near-surface nitrogen-vacancy (NV) centers have been created in diamond through low energy implantation of 15N to sense electron spins that are external to the diamond. By performing double resonance experiments, we have verified the presence of g=2 spins on a diamond crystal that was subjected to various surface treatments, including coating with a polymer film containing the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH). Subsequent acid cleaning eliminated the spin signal without otherwise disrupting the NV center, providing strong evidence that the spins were at the surface. A clear correlation was observed between the size of the detected spin signal and the relaxation time T2 for the six NV centers studied. We have developed a model that takes into account the finite correlation time of the fluctuating magnetic fields generated by the external spins, and used it to infer the signal strength and correlation time of the magnetic fields from these spins. This model also highlights the sensitivity advantage of active manipulation of the longitudinal spin component via double resonance over passive detection schemes that measure the transverse component of spin.