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 nanophotonic applications. Most recently, optically addressable spin qubits in h-BN have been the focus of intensive research due to their unique potential in quantum computation, 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 to show that out-of-plane XNYi dimer defects (X, Y = C, N, P, and Si) form a new class of stable C-3v spin-triplet defects in h-BN. We find that the dimer defects have a robust (3)A(2) ground state and E-3 excited state, both of which are isolated from the h-BN bulk states. We show that E-1 and (1)A shelving states exist and they are positioned between the E-3 and (3)A(2) states for all the dimer defects considered in this study. To support future experimental identification of the XNYi dimer defects, we provide extensive characterization of the defects in terms of their spin and optical properties. We predict that the zero-phonon line of the spin-triplet XNYi defects lies in the visible range (800 nm to 500 nm). We compute the zero-field splitting of the dimers' spin to range from 1.79 GHz (SiNPi0) to 29.5 GHz (CNNi0). 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.