Statistics of energy spectra of a strongly disordered system of interacting electrons

The statistics of many-particle energy levels of a finite two-dimensional s ystem of interacting electrons is studied numerically. It is shown that the statistics of these levels undergoes a Poisson-to-Wigner crossover as the strength of the disorder is decreased. This crossover occurs at a similar s trength of disorder to the one-electron delocalization crossover in a finit e two-dimensional system and develops almost simultaneously at all energies . We interpret this crossover in terms of delocalization in the space of oc cupation numbers of strongly bound and compact electron-hole pairs (exciton s).