Bias dependence of W, Mo and Ta conductance histograms

The increase of the bias voltage Vb above 0.4–0.5V results in the emerging of new peaks in the conductance histograms of W, Mo and Ta. Only for Ta and for some of the Mo contacts these peaks are reproducible and related to stable atomic arrangements. For W the additional peaks are always contact specific. The shape of the conductance histogram at elevated Vb depends also on the bias voltage and is changing in the process of measurements for the majority of Mo contacts. Possible reasons for this non-typical behavior of conductance of molybdenum and tungsten nanocontacts are discussed.