Investigation of the transport properties of gold point contacts

Electrical resistance, thermal resistance and thermoelectric power of gold point contacts with well-defined surface properties are investigated in the temperature range 2-300 K. The electrical contact resistance is temperature independent, the thermopower strongly decreases with reduction of the contact size, and an asymmetric heat release, expected for ballistic charge transport, is not detected. We conclude that electronic transport in microcontacts made of gold is strongly afflicted by surface layers. Even a monoatomic layer of impurity atoms creates a tunneling barrier that prevents ballistic carrier transport. Earlier experiments on the transport properties of mechanical point contacts are critically reviewed and discussed with respect to the present results.