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

在扫描隧道显微镜(STM)中，通过将尖端接触到金属表面，然后将尖端从金属表面拉出，形成原子尺寸的磁性金属丝。这些导线的电子传导既取决于包括自旋态在内的电子态，也取决于导线周围的原子排列。在本研究中，我们发展了一种测量4.2K至室温下清洁表面的超高真空电导率的方法，并测量了铁丝和镍丝的电导。我们用电子轰击的方法在现有的扫描隧道显微镜系统上添加了一个温度高达1200℃的退火基，以制备清洁的金属单晶，如镍。我们还设计并制作了一台用于电子电导研究的新型扫描隧道显微镜。我们测量了铁纳米线的电导作为表面和STM针尖之间位移的函数。对观测到的电导曲线进行了量子化处理，发现电导曲线的某些阶跃在重复位移时存在滞后现象。在没有自旋简并的铁磁材料中，量子化的单位是预期的e^2/h。电导的磁场依赖性一般很小，直到150mT。在表面和STM针尖之间的位移变化过程中，只有当导线的长度固定在接近电导台阶的位置时，才会通过改变磁场来出现电导台阶。这主要归因于磁致伸缩效应。比较了在镍单晶和镍薄膜上的结果。我们发现，磁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.