Enhancement of shot noise due to the fluctuation of Coulomb interaction

Abstract

For a resonant tunneling structure, it was found experimentally that the shot noise is super-Poissonian in the negative differential region (NDR). From a semiclassical analysis, it is believed that the super-Poissonian behavior is due to fluctuation of the Coulomb interaction. Although there are many studies on shot noise in mesocopic or nanoscale systems, an accounting by first-principles quantum transport theory for super-Poissonian behavior in the NDR is still lacking. In this paper, we develop a theoretical formalism to investigate the contribution of fluctuations of the Coulomb interaction to the shot noise, based on the Keldysh nonequilibrium Green's function method. We applied our theory to study the behavior of dc shot noise of atomic junctions, using the method of nonequilibrium Green's functions combined with density functional theory (NEGF-DFT). In particular, for an atomic carbon wire consisting of four carbon atoms in contact with two Al(100) electrodes, a first-principles calculation within the NEGF-DFT formalism shows a NDR region in the I-V curve at finite bias due to the effective band bottom of the Al lead. We calculated the shot noise spectrum using our theory. Our numerical result shows super-Poissonian behavior with a Fano factor larger than 1 in the NDR region, in agreement with the experimental result. © 2012 American Physical Society.