Many-exciton effects in the biexciton bound-state potential

S.A. Moskalenko

Monique Combescot, R. Combescot

When a direct-gap semiconductor is irradiated in the transparency region, the exciton line blue shifts. This so-called optical Stark effect of the exciton is due to a coupling between the exciton and all biexcitonic states (bound or unbound). More precisely we show that the exciton shift results only from interactions between excitons (Coulomb interaction and Pauli exclusion). At large detuning, Pauli exclusion dominates, and the excitonic shift is the same as the dressed-atom blue shift. In material having a bound biexcitonic molecule, the excitonic blue shift, observed at large detuning, becomes a red shift at small detuning close to the exciton-biexciton resonance.

S. A. Moskalenko

Arturo Argüelles, Luis Santos

We show that the interplay between spin-changing collisions and quadratic Zeeman coupling provides a mechanism for the formation of repulsively bound composites in high-spin fermions, which we illustrate by considering spin flips in an initially polarized hard-core one-dimensional Mott insulator of spin-$3/2$ fermions. We show that after the flips the dynamics is characterized by the creation of two types of exciton-biexciton composites. We analyze the conditions for the existence of these bound states and discuss their intriguing properties. In particular we show that the effective mass and stability of the composites depends nontrivially on spin-changing collisions, on the quadratic Zeeman effect, and on the initial exciton localization. Finally, we show that the composites may remain stable against inelastic collisions, opening the possibility of interesting quantum composite phases.

N. M. Belyĭ, Ivan S. Gorban, V. A. Gubanov +1 more

Daniele Hulin, M. Joffre

We report the observation of an exciton redshift with a below-gap laser beam, linked to the presence of a bound two-pair state in CuCl. This change in the shift direction for the optical Stark effect in semiconductors relies upon the predominant creation of virtual biexcitons, as shown by the polarization selection rules. Our experiment demonstrates the importance of the biexciton in the description of the optical Stark effect.