Kilohertz electron paramagnetic resonance spectroscopy of single nitrogen centers at zero magnetic field
Science Advances 6(22):eaaz8244 May 2020 

Kong, Fei; Zhao, Pengju; Yu, Pei; Qin, Zhuoyang; Huang, Zhehua; Wang, Zhecheng; Wang, Mengqi; Shi, Fazhan; Du, Jiangfeng


Electron paramagnetic resonance (EPR) spectroscopy is among the most important analytical tools in physics, chemistry, and biology. The emergence of nitrogen-vacancy (NV) centers in diamond, serving as an atomic-sized magnetometer, has promoted this technique to single-spin level, even under ambient conditions. Despite the enormous progress in spatial resolution, the current megahertz spectral resolution is still insufficient to resolve key heterogeneous molecular information. A major challenge is the short coherence times of the sample electron spins. Here, we address this challenge by using a magnetic noise–insensitive transition between states of different symmetry. We demonstrate a 27-fold narrower spectrum of single substitutional nitrogen (P1) centers in diamond with a linewidth of several kilohertz, and then some weak couplings can be resolved. Those results show both spatial and spectral advances of NV center–based EPR and provide a route toward analytical (EPR) spectroscopy at the single-molecule level. 

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