Current fluctuations in an ideally conducting contact

It is shown that the shot noise at finite frequency in an ideally conductin g contact is finite. The complete formula for the current correlation funct ion at finite frequency is presented for a quantum conductor, where the ele ctron transport can be adequately described in a model of noninteracting el ectrons using a scattering matrix. It is indicated that the description of electron transport in Landauer's approach (using a scattering matrix) is eq uivalent to a description using the Keldysh technique. Noise in an ideally conducting contact is calculated using the general formula. It is shown tha t in such a contact the spectral density of the noise has a singularity at the "Josephson" frequency omega=eV/(h) over bar, set by the voltage. (C) 19 99 American Institute of Physics. [S0021-3640(99)01015-4].