Absence of magnetically induced fractional quantization in atomic contacts

When a metallic wire is stretched its conductance becomes smaller as a result of the decrease of its cross section. This process continues until the breaking of the wire, and just before this event takes place, the contact is formed by just one atom. In this way atomic-sized contacts between two metallic electrodes can be formed and studied. The instruments that have made these studies possible are the mechanically controllable break junctions and the scanning tunneling microscope. In both techniques the relative displacement of two electrodes is controlled with a resolution of a few picometers by the use of a piezoelectric element which allows us to monitor the formation and breaking of the contact between the two electrodes. Properties of such atomic-sized contacts have been extensively studied during the past decade 1 for many different metals both magnetic and nonmagnetic. The conductance of these contacts can be described by the Landauer formula