Negative 4-Probe Conductances of Mesoscopic Superconducting Wires
  We analyze the longitudinal 4-probe conductance of mesoscopic normal and superconducting wires and predict that in the superconducting case, large negative values can arise for both the weakly disordered and localized regimes. This contrasts sharply with the behaviour of the longitudinal 4-probe conductance of normal wires, which in the localized limit is always exponentially small and positive. 
SJ Robinson, CJ Lambert and M Jeffery