Regensburg 2007 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 36: Heterostructures

HL 36.1: Vortrag

Donnerstag, 29. März 2007, 10:00–10:15, H14

Exciton-exciton interaction in coupled quantum wells: Quantifying conditions for Bose-Einstein condensation — •Christoph Schindler and Roland Zimmermann — Institut für Physik der Humboldt-Universität zu Berlin, Newtonstr. 15, 12489 Berlin, Germany

Spatially indirect electron-hole pairs in coupled quantum wells (CQW) have a reduced Coulomb attraction across the barrier, leading to a small binding energy of the indirect exciton. The repulsion between equal charges (electrons and holes), however, remains strong. Consequently, the interaction between two indirect excitons is dominated at large distances d by a strong dipole-dipole repulsion. Using CQW parameters for the GaAs/AlGaAs system we investigate the XX interaction as a function of d, improving the usual Hartree-Fock approach towards a full solution of the four particle problem. At small d, the fermionic exchange leads to a hard-core repulsive behavior, while at intermediate d van-der-Waals forces appear (depending on the singlet or triplet spin configuration). However, for realistic CQW parameters, no bound state (excitonic molecule) is formed. The generated XX potential is used to calculate XX scattering phase shifts and subsequently a full T matrix which is at the core for describing the approach towards Bose-Einstein condensation of indirect excitons.