Optical Stark effect in type-II semiconductor heterostructures

Charge-transfer excitons feature a permanent dipole moment introduced by the spatial charge separation of electron and hole wave functions. This directly influences and qualitatively modifies the coherent nonlinear optical response monitored in high-quality (Ga, In)As/Ga(As, Sb) type-II heterostructures through an opticalpump optical-probe experiment. A microscopic analysis based on the semiconductor Bloch equations reveals that the spatial inhomogeneity native to such type-II heterostructures introduces already on the Hartree-Fock a finite coupling between excitons of opposite spins which is pivotal for optical Stark effect experiments. This result in a blueshift of the charge-transfer exciton when pumping below the resonance for both, co-circular and counter circular polarization configurations, contrary to well-known and observed shifts of spatially direct exciton resonances.