Optically polarizable nitrogen-vacancy (NV) center in diamond enables the hyperpolarization of 13C nuclear spins at low magnetic field and room temperature. However, achieving a high level of polarization comparable to conventional dynamic nuclear polarization has remained challenging. Here we demonstrate that, at below 10 mT, a 13C polarization of 5 % can be obtained, equivalent to an enhancement ratio over 7×106. We used high-purity diamond with a low initial nitrogen concentration (< 1 ppm), which also results in a long storage time exceeding 100 minutes. By aligning the magnetic field along [100], the number of NV spins participating in polarization transfer increases fourfold. We conducted a comprehensive optimization of field intensity and microwave (MW) frequency-sweep parameters for this field orientation. The optimum MW sweep width suggests that polarization transfer occurs primarily to bulk 13C spins through the integrated solid effect followed by nuclear spin diffusion.
@article{arxiv.2409.19489,
title = {Achieving 5 % $^{13}$C nuclear spin hyperpolarization in high-purity diamond at room temperature and low field},
author = {Vladimir V. Kavtanyuk and Changjae Lee and Keunhong Jeong and Jeong Hyun Shim},
journal= {arXiv preprint arXiv:2409.19489},
year = {2024}
}