RESUMO
Optically active point defects in semiconductors have received great attention in the field of solid-state quantum technologies. Hexagonal boron nitride, with an ultra-wide band gapEg= 6 eV, containing a negatively charged boron vacancy (VB-) with unique spin, optical, and coherent properties presents a new two-dimensional platform for the implementation of quantum technologies. This work establishes the value ofVB-spin polarization under optical pumping withλext= 532 nm laser using high-frequency (νmw= 94 GHz) electron paramagnetic resonance (EPR) spectroscopy. In optimal conditions polarization was found to beP≈ 38.4%. Our study reveals that Rabi oscillations induced on polarized spin states persist for up to 30-40µs, which is nearly two orders of magnitude longer than what was previously reported. Analysis of the coherent electron-nuclear interaction through the observed electron spin echo envelope modulation made it possible to detect signals from remote nitrogen and boron nuclei, and to establish a corresponding quadrupole coupling constantCq= 180 kHz related to nuclear quadrupole moment of14N. These results have fundamental importance for understanding the spin properties of boron vacancy.
RESUMO
Optically addressable high-spin states (S ≥ 1) of defects in semiconductors are the basis for the development of solid-state quantum technologies. Recently, one such defect has been found in hexagonal boron nitride (hBN) and identified as a negatively charged boron vacancy (VB-). To explore and utilize the properties of this defect, one needs to design a robust way for its creation in an hBN crystal. We investigate the possibility of creating VB- centers in an hBN single crystal by means of irradiation with a high-energy (E = 2 MeV) electron flux. Optical excitation of the irradiated sample induces fluorescence in the near-infrared range together with the electron spin resonance (ESR) spectrum of the triplet centers with a zero-field splitting value of D = 3.6 GHz, manifesting an optically induced population inversion of the ground state spin sublevels. These observations are the signatures of the VB- centers and demonstrate that electron irradiation can be reliably used to create these centers in hBN. Exploration of the VB- spin resonance line shape allowed us to establish the source of the line broadening, which occurs due to the slight deviation in orientation of the two-dimensional B-N atomic plains being exactly parallel relative to each other. The results of the analysis of the broadening mechanism can be used for the crystalline quality control of the 2D materials, using the VB- spin embedded in the hBN as a probe.