Probing spin-phonon interaction of boron-vacancy centers in hexagonal boron nitride

The negatively charged boron-vacancy center (V_B^-) in hexagonal boron nitride (hBN) has recently emerged as a highly promising quantum sensor due to its ability to integrate with heterogeneous devices. Compared to the nitrogen-vacancy (NV) center in diamond, the temperature dependence of the spin transition energy of V_B^- is more than an order of magnitude greater, but the underlying mechanism has not been fully understood. We first use isotopically purified h¹⁰B¹⁵N to systematically characterize the zero-field splitting, hyperfine interaction, and spin relaxation time of V_B^- from 10 to 350 K. Our first-principle calculations of the VB- spin-phonon interaction show good agreement with experimental data. We found that a second-order effect from finite-temperature phonon excitations is the main contributor to the observed behavior. These temperature-dependent properties allow V_B^- to detect local phonon modes of its host and neighboring materials in heterogeneous devices, enabling a novel sensing modality that is unique to quantum sensors in 2D materials.