Bias dependence of the conductance of Au nanocontacts

The bias dependence of the quantized conductance in Au relay contacts has been studied by measuring the transient conductance in the contact break. Au nanocontacts are known to exhibit sharp peaks in their conductance histograms at and near the quantized positions ${\mathrm{nG}}_0$ ${(G}_0{=2e}^2/h$ and $n=1,2,3,\dots ).\mathrm{}$ With increasing the bias, we find that the ${1G}_0$ peak height decreases almost linearly, while the peak position shows no shift and stays at $0.96\pm {0.02G}_0.$ The ${2G}_0$ peak height also decreases with the bias, and its bias dependence agrees with that of the ${1G}_0$ peak when the bias is normalized by the disappearance voltage of each peak. We have also measured the distribution of the ${1G}_0$ plateau length (duration) at various biases and find that the distribution becomes reduced at high biases. However, a small number of plateaus survive even at 2 V, and the average plateau length remains almost bias independent for biases greater than 1.2 V. This result indicates that the suppression of the ${1G}_0$ peak height at high biases is due to the decrease, not in the plateau lifetime, but in the plateau formation probability. The bias dependence of the ${1G}_0$ plateau formation is discussed with its relation to the nonlinear conductance in Au nanocontacts.