First-principles predictions of out-of-plane group IV and V dimers as high-symmetry high-spin defects in hexagonal boron nitride*

Hexagonal boron nitride (h-BN) has been recently found to host a variety of quantum point defects, which are promising candidates as single-photon sources for solid-state quantum nanophotonics applications. Most recently, optically addressable spin qubits in h-BN have been the focus of intensive research due to their unique potential in quantum computing, communication, and sensing. However, the number of high-symmetry high-spin defects that are desirable for developing spin qubits in h-BN is highly limited. Here, we combine density functional theory (DFT) and quantum embedding theories (QET) to show that out-of-plane X_NY_i dimer defects (X, Y=C, N, P, Si) form a new class of stable C_3v spin-triplet defects in h-BN. We find that the dimer defects have a robust ³A₂ ground state and ³E excited state, both of which are isolated from the h-BN bulk states. We show that ¹E and ¹A shelving states exist and they are positioned between the ³E and ³A₂ states for all the dimer defects considered in this study. To support future experimental identification of the X_NY_i dimer defects, we provide an extensive characterization of the defects in terms of their spin and optical properties. We predict that the zero-phonon line of the spin-triplet X_NY_i defects lies in the visible range (800 nm – 500 nm) range. We compute the zero-field splitting of the dimers’ spin to range from 1.79 GHz (Si_NP_i⁰) to 29.5 GHz (C_NN_i⁰). Our results broaden the scope of high-spin defect candidates that would be useful for the development of spin-based solid-state quantum technologies in two-dimensional hexagonal boron nitride.