Quantized electronic conduction of metallic nanowire made in low-temperature scanning tunneling microscope

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Atomic-size wires of magnetic metals are formed in a scanning tunneling microscope (STM) by contacting the tip apex to the metal surface followed by withdrawing the tip from the surface. The electronic conduction of these wires depends both on the electronic states including spin states and on the atom arrangement around the wires. In the present study, we have developed a method to measure the conductivity between 4.2 K and room temperature in ultra high vacuum on clean surfaces, and measured the conductance of iron and nickel wires.1. We attached an annealing base up to 1200 degree G by electron bombardment to the present STM system to prepare clean surfaces of metal single crystals such as Ni. We also designed and made a new STM for the study of the electronic conduction.2. We measured the conductance of the iron nanowires as a function of the displacement between the surface and the STM tip. The observed conductance curves were quantized, and some steps in the conductance curves have hysteresis for repeated displacements. The unit of the quantization is e^2/h as expected in ferromagnetic materials without spin degeneracy. The magnetic field dependence of the conductance is generally small up to 150 mT. Only when the length of the wire is fixed close to the conductance step during the change of the displacement between the surface and the STM tip, the conductance step appears by changing the magnetic field. This is attributed to the effect of magnetostriction.3. The results on Ni single crystal is compared with those on Ni thin films. We found the magnetoresitance is dependent on the magnetization process of the substrate.