THEORETICAL INVESTIGATION OF QUANTUM TRANSPORT PHENOMENA IN AN ATOM BRIDGES CONSTRUCTED BETWEEN AN STM TIP AND A METAL SURFACE

STM 尖端和金属表面之间构建的原子桥中量子输运现象的理论研究

基本信息

批准号：
11640375
负责人：
KASAI Hideaki
金额：
$ 2.43万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2002
项目状态：
已结题

项目摘要

When a scanning tunneling microscope (STM) tip is brought into contact with a metal surface and then lifted up, an atom-sized contact (point contact) is formed between the tip and the surface. As the tip is further lifted up, by about less than a few nanometers from the surface, an atom-sized wire (a few-atoms across in dimensions) is formed between the STM tip and the metal surface. Because the electrons are confined in the direction normal to the atom bridge axis, the atom bridge exhibits quantized conductance. We have investigated the quantum transport phenomena observable in these atom-sized bridges, made from magnetic materials, using the single-band Hubbard model. We found that, at finite temperatures, because of inter-subband scattering, which originates from the strong electron Coulomb interaction, the corresponding Conductance (G) vs. Length plot shows deviations from the characteristic step-like structure, particularly in the transition region between a conductance plateau an … More d a conductance step. We have also proposed a method on how, using the STM tip, we could manipulate the magnetic and quantum transport properties of these atom bridges. By performing first-principles calculations, we have also determined the possible stable structures for Fe atom bridges, one and two atoms across in dimensions. Furthermore, we have determined how we could control/manipulate the magnetic and quantum transport properties of these atom bridges by changing the composition of the atom wire through alloying and obtain, e.g., atom wires with specific spin polarization ratios of the electric current flowing through them. Consider for example an FeαNi1-α, atom bridge. We found that this alloyed atom bridge exhibits a magnetic moment considerably larger than that predicted by the Pauling-Slater curve for bulk materials. Furthermore, we have determined that the minority spin contribution to the corresponding atom bridge conductance strongly depends on the Ni concentration, although the majority spin contribution remains the same. These properties are determined by the energetic variations in the corresponding s- and d-bands. Thus, a technology based on information gained from this study would provide us with a novel means of designing and realizing functional ballistic spin conductors. Less

当扫描隧道显微镜（STM）尖端与金属表面接触然后抬起时，随着尖端进一步抬起大约，在尖端和表面之间形成原子大小的接触（点接触）。在距离表面不到几纳米的地方，STM 尖端和金属表面之间形成了一条原子大小的线（尺寸为几个原子），因为电子被限制在垂直于原子桥轴的方向上。原子桥展品我们使用单带哈伯德模型研究了这些由磁性材料制成的原子大小的桥中可观察到的量子输运现象，我们发现，在有限温度下，由于子带间散射而产生的现象。由于强电子库仑相互作用，相应的电导 (G) 与长度图显示了与特征阶梯结构的偏差，特别是在电导平台和电导阶梯之间的过渡区域。提出了一种如何使用 STM 尖端操纵这些原子桥的磁性和量子传输特性的方法，通过执行第一性原理计算，我们还确定了铁原子桥（一个和两个原子跨过）的可能稳定结构。此外，我们还确定了如何通过合金化改变原子线的成分来控制/操纵这些原子桥的磁性和量子传输特性，并获得例如具有特定自旋极化比的原子线。以 FeαNi1-α 原子桥为例，我们发现这种合金原子桥的磁矩明显大于块体材料的鲍林-斯莱特曲线所预测的磁矩。尽管多数自旋贡献保持不变，但少数自旋对相应原子桥电导的贡献很大程度上取决于相应 s 和 d 带的能量变化。关于信息这项研究的成果将为我们提供一种设计和实现功能性弹道自旋导体的新方法。