Effect of surface contact potential in atomic-size contacts

•We perform a mechanical break junction (MBJ) experiment to study quantized conductance in atomic-size Au contacts.•Our conductance histogram shows a slight shift from integer multiples, consistent with previous reports.•KPM shows that the surface potential distribution of a real metal is highly non-uniform and is strongly distance-dependent.•An induced current through capacitive coupling is shown to be responsible for the observed conductance shift.

We present a study of the effect of surface contact potential in a mechanical break junction experiment. Using amplitude-modulated Kelvin probe microscopy (KPM), we show that the surface potential of a real metal is highly non-uniform and is strongly distance-dependent. Based on our KPM results, we propose a model in which a current is induced from the capacitive coupling of the surface potential and accounts for much of the observed shifts of the conductance peaks from integer multiples. The significance of our results in other areas of physics is also discussed.