Highly nonlinear excitonic Zeeman spin splitting in composition-engineered artificial atoms

Nonlinear Zeeman splitting of neutral excitons is observed in composition-engineered In _xGa _1-xAs self-assembled quantum dots, and its microscopic origin is explained. Eight-band k•p simulations, performed using realistic dot parameters extracted from cross-sectional scanning tunneling microscopy measurements, reveal that a quadratic contribution to the Zeeman energy originates from a spin-dependent mixing of heavy- and light-hole orbital states in the dot. The dilute In composition (x<0.35) and large lateral size (40-50 nm) of the quantum dots investigated are shown to strongly enhance the nonlinear contribution to the excitonic Zeeman gap, providing a blueprint to enhance such magnetic nonlinearities via growth engineering of the quantum dots.