Conductance of single-atom platinum contacts: Voltage-dependence of the   conductance histogram
  The conductance of a single-atom contact is sensitive to the coupling of this contact atom to the atoms in the leads. Notably for the transition metals this gives rise to a considerable spread in the observed conductance values. The mean conductance value and spread can be obtained from the first peak in conductance histograms recorded from a large set of contact-breaking cycles. In contrast to the monovalent metals, this mean value for Pt depends strongly on the applied voltage bias and other experimental conditions, ranging from about 1 to 2.5 times 2e^2/h. We propose that the different results in part can be explained by the inclusion of hydrogen in the contacts. The bias dependence of the conductance is on the other hand due to the electron current that destabilizes monatomic Pt chains at high bias. 
S.K. Nielsen, Y. Noat, M. Brandbyge, R.H.M. Smit, K. Hansen, L.Y.   Chen, A.I. Yanson, F. Besenbacher and J.M. van Ruitenbeek