LATERAL MOTION OF CONFINED EXCITONIC POLARITONS

Transient-grating measurements on high-quality ZnSe/ZnSxSe1-x heterost ructures reveal a strong increase of the lateral polariton-transport c oefficient with the ZnSe thickness L in a range from 5 to 30 excitonic Bohr radii. In this weak-confinement regime a strict quantization of the polariton-wave-vector component k(z) normal to the layer occurs, a s is experimentally verified for our samples. On this basis, it is sho wn by use of polariton theory that the observed increase of the latera l transport coefficient can be explained by an intrinsic drastic incre ase of the lateral polariton group velocity. This is caused by a trans ition from quasiexcitonic to polaritonic transport when the first quan tized mode with k(z)(l)=tau/L passes through the bottleneck region of the lower polariton branch for increasing L. [S0163-1829(98)00515-3].