New study of shot noise with the nonequilibrium Kubo formula in mesoscopic systems, application to the Kondo effect at a quantum dot
Abstract
Recently we have developed a theory of Keldysh formalism for mesoscopic systems. The resulting nonequilibrium Kubo formula for differential conductance makes it possible to propose the new formula of shot noise Sh, and thus to study shot noise in correlated systems at any temperature and any bias voltage. Employing this new approach, we analyze shot noise in the Kondo regime through a quantum dot for the symmetric case at zero temperature. Using the renormalized perturbation theory, we prove that in the leading order of bias voltage Sh equal to noise power at zero temperature conventionally used as shot noise. With Sh, we calculate the Fano factor for a backscattering current Ib: Fb=Sh/2eIb. It is shown that the Fano factor takes the universal form of Fb=1+4(R-1)2/(1+5(R-1)2) determined by the Wilson ratio R for arbitrary strength of the Coulomb interaction. Using the Wilson ratio R=2, our result coincides with the fractional value of Fb=5/3 already derived in the Kondo regime.