QUANTUM FLUCTUATIONS IN GRANULAR METALS

A new model of 3D quantum chaotic billiards is used to investigate glo bal quantum fluctuations in metallic particles. The quantum system is described by means of a tight-binding Hamiltonian, in which the energi es of the orbitals at the surface sites are chosen at random between - 1/2 W and 1/2 W. The results indicate that for values of W of the orde r of half the bandwidth, the fluctuations of the highest occupied leve l are already much larger than the corresponding average interlevel sp acing. This provides a natural explanation for autoionization effects in granular metals. The model shows diffusive or ballistic behavior de pending on the value of W, as observed in the energy fluctuations whic h are larger or smaller than GOE, for the respective behaviors.