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

当使扫描隧道显微镜（STM）针尖与金属表面接触然后抬起时，在针尖和表面之间形成原子大小的接触（点接触）。当针尖进一步提升时，距离表面约小于几纳米，在STM针尖和金属表面之间形成原子大小的线（尺寸上跨越几个原子）。由于电子被限制在垂直于原子桥轴的方向上，原子桥表现出量子化的电导。我们已经研究了在这些原子大小的桥梁，磁性材料制成，使用单带哈伯德模型中观察到的量子输运现象。我们发现，在有限温度下，由于强电子库仑相互作用引起的子带间散射，相应的电导（G）与长度的关系曲线显示出与特征台阶状结构的偏离，特别是在电导平台和长度之间的过渡区。 ...更多信息 d电导步骤。我们还提出了一种方法，如何使用STM针尖，我们可以操纵这些原子桥的磁性和量子输运性质。通过第一性原理计算，我们还确定了Fe原子桥的可能稳定结构，一维和二维原子。此外，我们已经确定了如何通过合金化改变原子线的组成来控制/操纵这些原子桥的磁性和量子输运性质，并获得例如，原子线具有特定的自旋极化率的电流流过它们。例如，考虑Feα Ni 1-α原子桥。我们发现，这种合金原子桥表现出的磁矩大大大于预测的Pauling-Slater曲线的散装材料。此外，我们已经确定，少数自旋贡献相应的原子桥电导强烈依赖于镍浓度，虽然多数自旋贡献保持不变。这些性质是由相应的s-和d-波段的能量变化决定的。因此，基于从这项研究中获得的信息的技术将为我们提供一种设计和实现功能弹道自旋导体的新方法。少

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