Spontaneous Shape Distortion in Quench-Condensed Bismuth Clusters below 8 K

We study single-electron transport in quench-condensed bismuth films. By lateral confinement, we select a specific cluster of about ${10}^3$ atoms and use tunneling barriers that appear naturally during thin-film formation. A remarkable reversible increase of the sample conductance up to 5 times was found as the temperature was lowered from 11 to 4 K. We attribute this effect to a spontaneous distortion of the cluster shape and discuss its relation to a phase transition predicted for free metallic clusters.