The negatively charged boron vacancy (V_B^-) in hexagonal boron nitride (hBN) is a well-established optically addressable spin defect in a van der Waals host, relevant for coherent spin dynamics, electron-nuclear interactions in two-dimensional materials, and atomically thin quantum sensing. We study electron spin echo envelope modulation (ESEEM) in this system using W-band Hahn-echo measurements at B₀~3.2 T, aligned along the hexagonal c-axis which is the principal axis of the V_B^- zero-field-splitting D-tensor. In this canonical high-field orientation, the electron-nuclear spin Hamiltonian is naturally secular, and the hyperfine (HF) interaction with the in-plane nearest-neighbor ¹⁴N nuclei is reduced mainly to its longitudinal projection along B₀. First-order ESEEM is therefore expected to be suppressed because the transverse pseudo-secular HF terms vanish by symmetry. We show that this expectation is incomplete because the nearest-neighbor ¹⁴N nuclear quadrupole (NQ) interaction axis lies approximately in the basal plane, nearly orthogonal to the field-defined quantization axis. The relatively large NQ coupling mixes the nuclear Zeeman states, while the longitudinal HF shift makes this mixing electron-spin dependent. The resulting non-commuting nuclear Hamiltonians produce finite Hahn-echo modulation even in the canonical high-field regime. Keywords: optically addressable spin defects in solids, boron nitride.

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Дата начала обработки статистических данных - 27 января 2016 г.