Bose condensation of excitonic molecules in CdSe

The Bose condensation of many exciton system is observed experimentally for the first time. It is found that excitonic molecules in CdSe exhibit the Bose condensation when the excitation is given at 1.8∼4.2 K by pico-second light pulses from a model-locked neodymium glass laser. This is concluded from the experimental facts that (1) an extremely sharp luminescence line attributed to originate from the k =0 condensed excitonic molecules is observed, (2) this sharp line is accompanied by the side-band on the low energy side and the spectrum is well understood by the theory developed by one of the authors, and (3) this line is produced within a limited range of excitation density which is wider at 1.8 K than at 4.2 K. Some arguments are presented on the importance of the use of the picosecond pulse excitation for the realization of the condensation.