Quantum interference in atomic-sized point contacts

Abstract

The conductance of atomic-sized metallic point contacts is shown to be strongly voltage dependent due to quantum interference with impurities even in samples with low impurity concentrations. Transmission through these small contacts depends not only on the local atomic structure at the contact but also on the distribution of impurities or defects within a coherence length of the contact. In contrast with other mesoscopic systems we show that transport through atomic contacts is coherent even at room temperature. The use of a scanning tunneling microscope ~STM! makes it possible to fabricate one atom contacts of gold whose transmission can be controlled by manipulation of the contact allowing inelastic spectroscopy in such small contacts. The conductance of atomic-sized contacts has been extensively studied in relation with the question of conductance quantization. Experimentally, the contacts are fabricated stretching a metallic contact using a scanning tunneling microscope 1 ~STM! or a mechanically controlled break junction ~MCBJ!. 2 Theoretically, the point contact has been modeled as a constriction for free electrons, 3,4 or a tight-binding model using different atomic arrangements. 5,6 Electronic transport in these nanoscopic size structures is coherent, and the conductance at zero bias voltage is given by the Landauer formula 7