Dynamic $^{14}\rm N$ nuclear spin polarization in nitrogen-vacancy centers in diamond

TL;DR

This study investigates the dynamic nuclear spin polarization of nitrogen in NV centers in diamond across a broad magnetic field range, revealing high polarization levels and sensitivity to magnetic field alignment, strain, and optical power.

Contribution

It provides comprehensive experimental and theoretical analysis of nuclear spin polarization in NV centers, especially near the ground-state level anti-crossing, with new insights into angular sensitivity and polarization efficiency.

Findings

Achieved up to 96% nuclear spin polarization over a broad magnetic field range.

Found that polarization is highly sensitive to magnetic field angle near the ground-state anti-crossing.

Demonstrated the effects of strain and optical power on polarization efficiency.

Abstract

We studied the dynamic nuclear spin polarization of nitrogen in negatively charged nitrogen-vacancy (NV) centers in diamond both experimentally and theoretically over a wide range of magnetic fields from 0 to 1100 G covering both the excited-state level anti-crossing and the ground-state level anti-crossing magnetic field regions. Special attention was paid to the less studied ground-state level anti-crossing region. The nuclear spin polarization was inferred from measurements of the optically detected magnetic resonance signal. These measurements show that a very large (up to $96 \pm 2\%$) nuclear spin polarization of nitrogen can be achieved over a very broad range of magnetic field starting from around 400 G up to magnetic field values substantially exceeding the ground-state level anti-crossing at 1024 G. We measured the influence of angular deviations of the magnetic field from the NV axis on the nuclear spin polarization efficiency and found that, in the vicinity of the ground-state level anti-crossing, the nuclear spin polarization is more sensitive to this angle than in the vicinity of the excited-state level anti-crossing. Indeed, an angle as small as a tenth of a degree of arc can destroy almost completely the spin polarization of a nitrogen nucleus. In addition, we investigated theoretically the influence of strain and optical excitation power on the nuclear spin polarization.