Supplemental material for Probing Remote Nuclear Magnetic Moments in hBN with V_B^- Electron Spin

This supplementary material provides additional insights into the analysis of hyperfine interactions of the V_B^- in hBN defects. It details the determination of the defect's principal axis orientation relative to an external magnetic field B0 applied perpendicular to the c-axis. Figure S1 presents a high-frequency 14N electron nuclear double resonance (ENDOR) spectrum and its simulation using a spin Hamiltonian parameter set with a deviation angle of 12{degree sign}, reproducing signals from the first coordination shell nuclei. The document further explores dynamic nuclear polarization (DNP) of distant ^14N nuclei via Hartmann-Hahn transfer from optically polarized V_B^- electron spins. Figure S2 presents the spin-lattice relaxation dynamics of the defect, revealing a relaxation time of T_1 ≈ 1.4 ms. Based on this measurement and a dipolar relaxation model, the nuclear spin-lattice relaxation time is estimated to be approximately T_1^nuc≈ 130 ms, indicating long nuclear spin memory and supporting the feasibility of efficient polarization transfer and retention.