Evidence for Saturation of Channel Transmission from Conductance Fluctuations in Atomic-Size Point Contacts

The conductance of atomic-size contacts has a small, random, voltage dependent component analogous to conductance fluctuations observed in diffusive wires. A new effect is observed in gold contacts, consisting of a marked suppression of these fluctuations when the conductance of the contact is close to integer multiples of the conductance quantum. Using a model based on the Landauer-B\"uttiker formalism, we interpret this effect as evidence that the conductance tends to be built up from fully transmitted (i.e., saturated) channels plus a single, which is partially transmitted.