Systematic investigation of dynamic nuclear polarization with boron vacancy in hexagonal boron nitride

TL;DR

This study systematically investigates the optically detected magnetic resonance spectra of boron vacancies in hexagonal boron nitride to understand dynamic nuclear polarization mechanisms and develop a quantitative model for their behavior.

Contribution

It provides a comprehensive experimental and theoretical analysis of ODMR spectra in hBN with V_B^- defects, advancing the understanding of DNP processes in this material.

Findings

Simulation reproduces experimental spectra including GSLAC.

Fitting methods do not yield accurate nuclear polarization estimates.

Symmetry effects limit maximum achievable polarization.

Abstract

Dynamic nuclear polarization (DNP) using the boron vacancy ($\mathrm{V_B^-}$) in hexagonal boron nitride (hBN) has gained increasing attention. Understanding this DNP requires systematically investigating the optically detected magnetic resonance (ODMR) spectra and developing a model that quantitatively describes its behavior. Here, we measure the ODMR spectra of $\mathrm{V_B^-}$ in $\mathrm{h}^{10}\mathrm{B}^{15}\mathrm{N}$ over a wide magnetic field range, including the ground state level anti-crossing (GSLAC), and compare them with the results of the Lindblad-based simulation that considers a single electron spin and three neighboring $^{15}\mathrm{N}$ nuclear spins. Our simulation successfully reproduces the experimental spectra, including the vicinity of GSLAC. It can explain the overall behavior of the magnetic field dependence of the nuclear spin polarization estimated using the Lorentzian fitting of the spectra. Despite such qualitative agreement, we also demonstrate that the fitting methods cannot give accurate polarizations. Finally, we discuss that symmetry-induced mechanisms of $\mathrm{V_B^-}$ limit the maximum polarization. Our study is an essential step toward a quantitative understanding of DNP using defects in hBN and its quantum applications.