Excitons in quantum dots: giant electron-hole long-range exchange interaction

Summary form only given. Exciton fine structure - typically a weak effect in bulk semiconductors (typical energies <1 meV for III-V and II-VI systems) - can dominate the spectroscopic properties of quantum dots. The correct assignment of the states appearing in the spectra is essential not only to understand the spectra themselves, but to identify relevant dephasing mechanisms and to model carrier relaxation between quantum-confined states. Meanwhile, the role of the electron-hole long-range exchange interaction is often misunderstood or underestimated. To that end we have undertaken an attempt to obtain the long-range-exchange-induced splittings in II-VI semiconductor nanocrystals. Within this approach the splittings arise due to interaction of the mechanical exciton with the exciton-induced macroscopic longitudinal electric field. Bright-to-dark exciton sublevel splittings in CdSe nanocrystals are shown as a function of nanocrystal radius.