Fig. 1: Integration of intrinsic spin defects in hBN metasurfaces.
From: Optically addressable spin defects coupled to bound states in the continuum metasurfaces
a Illustration of a symmetry broken qBIC optical metasurface fabricated from a single multilayer hBN crystal (top inset), on a glass substrate. The unit cell (bottom inset) is composed of two asymmetric rods. The asymmetry parameter is given by the difference ΔL in length between the two rods. b Illustration of the atomic structure of negatively charged boron vacancy defects (VB-, green arrows) depicted in a single layer of hBN. c Simplified energy level diagram of a VB- defect with the excited state (3E”), ground state (3A2’) and a metastable singlet state (MS). The qBIC acts as an optical cavity, resonantly enhancing the radiative transition of the coupled defect (gray arrow). d Electric dipole moments (p1, p2) and electric (E) field intensity for a symmetry broken unit cell, calculated at the qBIC resonance and excited with a plane wave linearly polarized parallel to the rod long axis. e Experimental PL spectrum of VB- defects (in purple) and transmission spectrum (T) of a high-Q factor metasurface resonance (in gray). f Numerical FDTD simulations of the transmission of hBN metasurfaces for different scaling factors (S). Tuning of the scaling factor, and therefore the corresponding unit cell size, shifts the qBIC resonance wavelength over a broad spectral range. g Numerical FDTD simulations of the transmission of hBN metasurfaces for different values of the asymmetry parameter ΔL. Increasing the asymmetry results in a blueshift of the qBIC resonance and a reduction of the Q factor. When ΔL = 0 nm, the qBIC state transforms into a dark BIC state, and no resonance is present (dashed black line).
