Conductance steps and quantization in atomic-size contacts

The conductance of metallic contacts of atomic size has been studied using a scanning tunneling microscope at low temperature. As the contact area is changed by pressing the tip into the sample, a series of reproducible features and jumps in the conductance at integer multiples of 2${\mathit{e}}^{2}$/h is observed. The jumps are interpreted as atomic rearrangements, while the underlying conductance structure strongly suggests quantum-size effects.