Effect of Screening on Shot Noise in Diffusive Mesoscopic Conductors

Shot noise in diffusive mesoscopic conductors, at finite observation frequencies ω (comparable to the reciprocal Thouless time τ-1T ), is analyzed with an account of screening. At low frequencies, the well-known result SI(ω)=2eI/3 is recovered. This result is valid at arbitrary ωτT for wide conductors longer than the screening length. However, at least for two very different systems, namely, wide and short conductors, and thin conductors over a close ground plane, noise approaches a different fundamental level, SI(ω)=eI , at ωτT>1 . copyright 1997 The American Physical Society