The role of boundary conditions in shot noise in elastic diffusive conductors

The role played by boundary conditions at a kinetic level in determining the noise properties of mesoscopic diffusive conductors is evaluated by decomposing the current fluctuations, into fluctuations of boundaries, self-consistent electric potential and the intrinsic Langevin source. We show that the self-consistent contribution is essentially controlled by the range of energies determined by the distribution function at the contacts together with the differential conductivity in energy space. The intrinsic contribution is completely determined by the boundary conditions and is expressed in closed analytical form in these terms. The present formulation provides a unifying microscopic approach of the noise properties of mesoscopic diffusive conductors showing that (i) in the absence of Coulomb interaction the Fano factor γ takes values bounded in the range (1/3)⩽γ⩽1 and (ii) in the presence of Coulomb interaction the values of γ are no longer bounded in the above range and enhanced shot noise becomes possible.