Current-Voltage Curves of Atomic-Sized Transition Metal Contacts: An Explanation of Why Au is Ohmic and Pt is Not

We present an experimental study of current-voltage ($I\text{−}V$) curves on atomic-sized Au and Pt contacts formed under cryogenic vacuum (4.2 K). Whereas $I\text{−}V$ curves for Au are almost Ohmic, the conductance $G=I/V$ for Pt decreases with increasing voltage, resulting in distinct nonlinear $I\text{−}V$ behavior. The experimental results are compared with first principles density functional theory calculations for Au and Pt, and good agreement is found. The difference in conductance properties for Pt vs Au can be explained by the underlying electron valence structure: Pt has an open $d$ shell while Au has not.