Resistance fluctuations in a four-probe geometry with infinite leads

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Abstract
The mean-square variation in the magnetoresistance of small metal wires is calculated in a four-probe geometry with infinite leads. Dephasing scattering is included in a simplified but current-conserving manner. As a result, a region of each lead approximately one dephasing length from the sample contributes to the fluctuations, which, however, then remain finite as the leads are made long, as one would expect on phyiscal grounds. The calculated symmetric and antisymmetric parts of the resistance fluctuations are in semiquantitative agreement with experiment.