Conductance Fluctuations in Microstructures for a Four-Probe Geometry

Recent work on conductance fluctuations in microstructures has revealed universal characteristics in the diffusive regime. However, quantitative microscopic calculation to date have dealt exclusively with the two-point conductance of a disordered region attached to two ordered leads. 

These calculations are appropriate only when the conductance is measured on a scale larger than an inelastic mean free path. However, recent experiments have probed length scales shorter than an inelastic mean free path and find significant new effects.