Triplet ground state and optical excitations of local defects in cubic BeS.

Our Density-Functional-Theory, GW, and Bethe-Salpeter calculations show that cubic BeS semiconductor is a promising host for local defects with potential applications in quantum technologies. By applying the postulate that defects leaving under-coordinated at least 3 atoms of relatively high electronegativity and changing the number of electrons by an even number favor triplet ground states, we have found that all 3 studied defects in BeS have a ground triplet state, are dynamically stable, and display intense optical excitations at sufficiently low energies (~0.5 eV) such that they may serve as spin qubits that do not require a non-radiative transition to an excited state of the corresponding singlet (still to be found) in order to complete the initialization spin-polarization cycle, but may directly decay to the ground state of the singlet state.

[1] Sergey Stolbov and Marisol Alcántara Ortigoza; Phys. Rev. B 109, L241108 (2024)