13C dynamic nuclear polarization in diamond via a microwave-free 'integrated' cross effect

TL;DR

This paper demonstrates a microwave-free method for dynamic nuclear polarization in diamond using NV and P1 centers, controlled by magnetic field sweeps, effective even with misaligned fields and heterogeneity.

Contribution

It introduces a novel microwave-free DNP technique leveraging magnetic field sweeps near the level anti-crossing in diamond with NV and P1 centers, enhancing robustness and potential applications.

Findings

Efficient 13C DNP achieved without microwaves.

Polarization sign and amplitude controlled by sweep rates.

Technique is robust to magnetic field misalignment.

Abstract

Color-center-hosting semiconductors are emerging as promising source materials for low-field dynamic nuclear polarization (DNP) at or near room temperature, but hyperfine broadening, susceptibility to magnetic field heterogeneity, and nuclear spin relaxation induced by other paramagnetic defects set practical constraints difficult to circumvent. Here, we explore an alternate route to color-center-assisted DNP using nitrogen-vacancy (NV) centers in diamond coupled to substitutional nitrogen impurities, the so-called P1 centers. Working near the level anti-crossing condition - where the P1 Zeeman splitting matches one of the NV spin transitions - we demonstrate efficient microwave-free 13C DNP through the use of consecutive magnetic field sweeps and continuous optical excitation. The amplitude and sign of the polarization can be controlled by adjusting the low-to-high and high-to-low magnetic field sweep rates in each cycle so that one is much faster than the other. By comparing the 13C DNP response for different crystal orientations, we show that the process is robust to magnetic field/NV misalignment, a feature that makes the present technique suitable to diamond powders and settings where the field is heterogeneous. Applications to shallow NVs could capitalize on the greater physical proximity between surface paramagnetic defects and outer nuclei to efficiently polarize target samples in contact with the diamond crystal.