Intersystem Crossing and Exciton-Defect Coupling of Spin Defects in Hexagonal Boron Nitride*

Despite the recognition of two-dimensional (2D) systems as emerging and scalable host materials of single photon emitters or spin qubits, uncontrolled and undetermined chemical nature of these quantum defects has been a roadblock to further development. Leveraging the design of extrinsic defects can circumvent these persistent issues and provide an ultimate solution. Here we established a complete theoretical framework to accurately and systematically design new quantum defects in wide-bandgap 2D systems. In particular, many-body interactions such as defect-exciton couplings are vital for describing excited state properties of defects in ultrathin 2D systems. Meanwhile, nonradiative processes such as phonon-assisted decay and intersystem crossing rates require careful evaluation, which compete together with radiative processes. From a thorough screening of defects based on first-principles calculations, we identified the Ti-vacancy complex as a promising defect in hexagonal boron nitride for spin qubits, with a triplet ground state, large zero-field splitting, and a prominent intersystem crossing rate highly desirable for spin-state initialization and qubit operation.

T. J. Smart, K. Li, J. Xu, and Y. Ping, arXiv:2009.02830 (2020).