Nuclear spin temperature reversal via continuous radio-frequency driving

TL;DR

This paper demonstrates how continuous RF driving can reverse nuclear spin polarization in diamond color centers, revealing complex spin dynamics and enabling new manipulation techniques for electron-nuclear systems.

Contribution

It uncovers a novel RF-driven spin reversal mechanism in diamond color centers, extending the understanding of hyperfine interactions and solid effect phenomena.

Findings

RF excitation causes sign reversal of nuclear spin signals

Modified solid effect observed at radio frequencies

Potential for manipulating multi-electron spin systems

Abstract

Optical spin pumping of color centers in diamond is presently attracting broad interest as a platform for dynamic nuclear polarization at room temperature, but the mechanisms involved in the generation and transport of polarization within the host crystal are still partly understood. Here we investigate the impact of continuous radio-frequency (RF) excitation on the generation of nuclear magnetization produced by optical illumination. In the presence of RF excitation far removed from the nuclear Larmor frequency, we witness a magnetic-field-dependent sign reversal of the measured nuclear spin signal when the drive is sufficiently strong, a counter-intuitive finding that immediately points to non-trivial spin dynamics. With the help of analytical and numerical modeling, we show our observations indicate a modified form of 'solid effect', down-converted from the microwave to the radio-frequency range through the driving of hybrid transitions involving one (or more) nuclei and two (or more) electron spins. Our results open intriguing opportunities for the manipulation of many-electron spin systems by exploiting hyperfine couplings as a means to access otherwise forbidden intra-band transitions.