Exchange coupling-assisted 13C dynamic nuclear polarization in microdiamond at 14 T
Q. Stern, J. Cui, R. Chaklashiya, C. Tobar, M. Judd, O. Nir-Arad, D. Shimon, I. Kaminker, H. Takahashi, J. R. Sirigiri, and S. Han Phys. Chem. Chem. Phys., 2026. https://doi.org/10.1039/D5CP04594K
We investigate nitrogen substitution defects, also known as P1 centers, in Type 1b diamonds generated under high pressure and high temperature (HPHT) as a source of electron spin polarization. The open question was how readily electron spin polarization in this diamond transfers to 13C nuclear spins within the diamond matrix at 14 T by dynamic nuclear polarization (DNP). The goal was to refine the model for clustered P1 centers in HPHT diamonds and evaluate their potential as a source for DNP hyperpolarization or contrast. The study relied on frequency-stepped measurements of DNP profiles under magic angle spinning (MAS) using the mm-wave output of a frequency-tunable gyrotron and a regular superconducting NMR magnet at a single field. We observe up to 700-fold 13C on/off signal enhancements in both MAS and static mode at room temperature, and 130-fold between 35 and 100 K. Modelling the experimental results revealed the dominant role of P1 clusters harboring inter-P1 dipolar and exchange couplings exceeding 100 MHz in achieving 13C DNP at 14.1 T. Our results exemplify the importance of exchange coupling for high-field DNP and provides a refined model for DNP via P1 centers of HPHT diamonds.