Influence of exciton-exciton interaction on quantum beats

Spectrally resolved four-wave mixing measurements in wurtzite GaN show a de pendence of the quantum beats' phase on incident polarizations. We observe different phases at the A-exciton and the B-exciton resonances when excitin g with circular polarized light. The observed phase difference indicates th at exciton-exciton interaction plays a major role in the quantum beat proce ss. The developed analysis allows us to conclude that the spins of the elec trons rather than the holes give the major contribution to the exciton-exci ton interaction in GaN.