Excited-state spin-resonance spectroscopy of V$${}_{{{{{{{{\rm{B}}}}}}}}}^{-}$$ defect centers in hexagonal boron nitride

Abstract

The recently discovered spin-active boron vacancy (V$${}_{{{{{{{{\rm{B}}}}}}}}}^{-}$$ B − ) defect center in hexagonal boron nitride (hBN) has high contrast optically-detected magnetic resonance (ODMR) at room-temperature, with a spin-triplet ground-state that shows promise as a quantum sensor. Here we report temperature-dependent ODMR spectroscopy to probe spin within the orbital excited-state. Our experiments determine the excited-state spin Hamiltonian, including a room-temperature zero-field splitting of 2.1 GHz and a g-factor similar to that of the ground-state. We confirm that the resonance is associated with spin rotation in the excited-state using pulsed ODMR measurements, and we observe Zeeman-mediated level anti-crossings in both the orbital ground- and excited-state. Our observation of a single set of excited-state spin-triplet resonance from 10 to 300 K is suggestive of symmetry-lowering of the defect system from D3h to C2v. Additionally, the excited-state ODMR has strong temperature dependence of both contrast and transverse anisotropy splitting, enabling promising avenues for quantum sensing.

Excited State Spectroscopy of Boron Vacancy Defects in Hexagonal Boron Nitride Using Time-Resolved Optically Detected Magnetic Resonance

“…21 Note: during the review of this manuscript, we became aware of related works studying the spin properties of the V B − excited state. 34,35 ■ ASSOCIATED CONTENT * sı Supporting Information…”

Spin-active defects in hexagonal boron nitride

“…Liu et al [197] measured the relationship between ground-state level and temperature (5K-600 K), which can be fitted using the Varshni empirical equation: 4(c)). Recently, the dependence of excited-state ODMR on temperature has also been experimentally measured [193,196]. It is noted that V − B defect will be destroyed in a high-temperature environment (>750 K) [191], which will limit the its scope of applications.…”

Strain Quantum Sensing with Spin Defects in Hexagonal Boron Nitride

“…The optical microscopy image of the h-BN flake, 133 ± 2 monolayers thick (see Supporting Information), deposited on the microwave stripline is shown in Figure b. A large number of bubbles (bright spots in Figure b) were generated during the deposition process, as often found in reports on transferred 2D materials, and were intentionally not removed by any postprocessing (or precleaning of the stripline), as they will be exploited to illustrate the strain sensitivity enabled by ODMR. The bubbles generated during the transfer process are typically 10 to 40 nm high, and 1 to 4 μm large (see Supporting Information for the atomic force microscopy images of bubbles 1 and 2 in Figure a), leading to much smaller strains than in voluntarily created bubbles. , Note that since the bubbles in Figures b and a are not necessarily gas-filled, but can be created by particles remaining on the stripline before the h-BN transfer, their form does not necessarily show spherical or radial symmetry (e.g., bubble1, which displays a triangular pyramidal form).…”

“…This asymmetric anistropic strain distribution might be related to the origin of our bubbles, which are created by the h-BN lying on top of microparticles and not by gas trapping. 31 Finally note that in order to give a quantitative estimation of the shear strain one would need to know the value of the c parameter for h-BN, which needs to be investigated in future research with controllable strain.…”