Properties of low-lying states in a diffusive quantum dot and lock-space localization

Motivated by an experiment of Sivan et al. and by subsequent theoretical wo rk on localization in Fock space, a hierarchical model is studied numerical ly for a finite many-body system of fermions moving in a disordered potenti al and coupled by a two-body interaction. Attention is focussed on the low- lying states close to the Fermi energy. Both the spreading width and the pa rticipation number depend smoothly on excitation energy. This behavior can be fully understood in terms of the density of available 1p-0h and 2p-1h st ates. The system does not display localization of Anderson type. The numeri cal model reproduces essential features of the experiment by Sivan et al.