Shot-noise current-current correlations in multiterminal diffusive conductors

We investigate the correlations in the current fluctuations at different terminals of metallic diffusive conductors. We start from scattering matrix expressions for the shot noise and use the Fisher-Lee relation in combination with diagram technique to evaluate the noise correlations. Of particular interest are exchange (interference) effects analogous to the Hanbury Brown-Twiss effect in optics. We find that the exchange effect exists in the ensemble-averaged current correlations. Depending on the geometry, it might have the same magnitude as the mean-square current fluctuations of the shot noise. The approach that we use is also applied to present a different derivation of the 1/3 suppression of shot noise in a two-terminal geometry, which is valid for an arbitrary relation between the length and wire width. We find that in all geometries correlations are insensitive to dephasing.