  Non-linear Zeeman splitting of neutral excitons is observed in composition
engineered In(x)Ga(1-x)As 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, 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 is shown to strongly enhance the non-linear excitonic Zeeman gap,
providing a blueprint to enhance such magnetic non-linearities via growth
engineering.
