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

点击翻译按钮获取中文摘要

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