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

在扫描隧道显微镜（STM）中，通过将针尖尖端与金属表面接触，然后将针尖从表面撤回，形成磁性金属的原子尺寸线。这些金属丝的电子导电性既取决于包括自旋态在内的电子态，也取决于金属丝周围的原子排列。在本研究中，我们开发了一种在超高真空中测量清洁表面4.2 K至室温之间电导率的方法，并测量了铁和镍导线的电导率。1.我们附加了一个退火基地高达1200度G的电子轰击到目前的STM系统，以准备清洁表面的金属单晶，如镍。我们还设计并制作了一台用于电子传导研究的新型STM.我们测量了铁纳米线的电导作为表面和STM尖端之间的位移的函数。电导曲线被量子化，电导曲线中的一些台阶对于重复位移具有滞后性。量子化的单位是e^2/h，正如在没有自旋简并的铁磁材料中所预期的那样。电导的磁场依赖性通常小到150 mT。只有当导线的长度固定在靠近电导台阶的位置时，在改变表面与STM针尖之间的位移时，才能通过改变磁场而出现电导台阶。这归因于磁致伸缩效应.对Ni单晶和Ni薄膜的结果进行了比较。我们发现磁电阻与衬底的磁化过程有关。

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.