Single-spin resonance in a van der Waals embedded paramagnetic defect

Abstract

Spins constitute a group of quantum objects forming a key resource in modern quantum technology. Two dimensional (2D) van der Waals materials are of fundamental interest for studying nanoscale magnetic phenomena. However, isolating singular paramagnetic spins in 2D systems is challenging. We report here on a quantum emitting source embedded within hexagonal boron nitride (h-BN) exhibiting optical magnetic resonance (ODMR). We extract an isotropic g-factor close to 2 and derive an upper bound for a zero field splitting (ZFS) (≤ 4 MHz).Photoluminescence )PL) behavior under temperature cycling using different excitations is presented, assigning probable zero phonon lines (ZPLs) / phonon side band (PSBs) to emission peaks, compatible with h-BN's phonon density of states, indicating their intrinsic nature. Narrow and in-homogenous broadened ODMR lines differ significantly from monoatomic vacancy defect lines known in literature. We derive a hyperfine coupling of around 10 MHz. Its angular dependence indicates an unpaired electron in an out of plane -orbital, probably originating from an additional substitutional carbon impurity or other low mass atom. We determine the spin relaxation time T1 to be around 17 s. Main TextVan der Waals two dimensional (2D) materials allow the isolation of one atomic monolayer to few layers of a crystal as thin as ~ 0.5 nm hosting a wealth of optically active defects. While a

Room-temperature optically detected magnetic resonance of single defects in hexagonal boron nitride

“…However, if all spin sublevels couple equally to the metastable state, the defects will show only one bunching timescale but no spin polarisation. Our model uses the same three-level structure as other reports 40 , 54 , but it should be noted that it also requires the addition of laser-power-dependent shelving and de-shelving rates.…”

“…However, the predicted hyperfine constants and the corresponding splitting for boron 55 isotopes differ starkly from our results. Potential single-carbon substitution defects, (C N and C B ) are predicted to show broadened resonances, rather than a distinct 30-MHz splitting 40 , 57 . Coupling to one C 13 nuclei could in principle result in a doublet, however the abundance of C 13 (~1%) does not reconcile with the yield of ODMR-active defects we measure (~5%) 57 .…”

“…Experimental and theoretical reports indicate that the structure of the defect is likely to contain carbon 40 , 47 , 59 – 63 . Defects in single crystalline hBN that show ODMR only under cryogenic conditions have been assigned to a spin- carbon substitution defect (C B ) 40 , 56 .…”

“…Experimental and theoretical reports indicate that the structure of the defect is likely to contain carbon 40 , 47 , 59 – 63 . Defects in single crystalline hBN that show ODMR only under cryogenic conditions have been assigned to a spin- carbon substitution defect (C B ) 40 , 56 . This defect emits at 730 nm and the ODMR shows a broad 40 MHz resonance, attributed to unresolved hyperfine coupling to neighbouring 11 B and 14 N nuclei 56 .…”

“…Multiple defect classes are emerging in hBN: a structure involving a single negatively charged boron vacancy (VB − ) displays broad emission at 800 nm and optically detected magnetic resonance (ODMR); however, this defect has only been measured on the ensemble level 35 – 38 . There are also individually addressable defects around 700 nm, where the presence of spin has been inferred via their magneto-optical signature 39 , and recently via cryogenic ODMR measurements in crystalline hBN 40 . A family of narrow-band bright emitters with distinctly sharper zero-phonon lines (ZPL) in the visible spectral range 41 – 52 has recently received more attention; they can be created controllably via chemical vapour deposition (CVD) 44 – 47 and plasma treatment methods 48 , display spectrally narrow bright optical emission 49 , and have already been integrated into optical cavities 50 – 52 .…”