Theoretical Study of Quantum Transport Phenomena through an Atom Sized Contact.

当扫描隧道显微镜的尖端与金属表面接触，然后慢慢抬起时，尖端和表面之间形成了原子大小的接触。这样就形成了一个原子大小的桥，它的横截面由几个原子到几十个原子组成。当顶端被抬起时，作为桥梁伸展长度的函数来测量桥梁的电导。电导的逐步变化在实验上大致以2e^&lt；&gt；h为单位。为了满足电子学中从介观尺度向原子尺度缩小的要求，有必要研究在这种原子尺度的系统中发生的各种现象。考虑到这一点，我们研究了原子大小的桥的束缚结构的影响，以及电子之间的库仑相互作用对通过原子大小的桥的量子化电导的影响。所获得的结果概括如下：1.…的紧致结构效应更多的是原子大小的桥：电导的阶梯变化被原子大小的桥形状的对称性破坏所干扰。电子之间的位内库仑相互作用的影响：在有限的温度下，库仑相互作用引起各种类型的电子-电子散射过程，子带间和子带内的散射过程和Umclapp以及正常的散射过程，并强烈地影响原子大小的桥的量子输运性质。结果表明：(1)在电导平台，随着温度的降低，电导值与普适值2e2/h的倍数的偏差增大；当库仑相互作用较强时，这种温度依赖性更强。(2)在台阶附近，出现一个山谷结构，它是桥梁伸展长度的函数。随着温度的降低，山谷变得更窄。随着库仑相互作用的加强，山谷的深度显著增加。较少

When the tip of a scanning tunneling microscope is brought into contact with a metal surface and then lifted up slowly, an atom-sized contact is formed between the tip and the surface. An atom-sized bridge is thus formed and its cross section consists of a few atoms to a few tens of atoms. Conductance of the bridge is measured as a function of the stretching length of the bridge, while the tip is lifted up. A stepwise variation of the conductance is experimentally observed roughly in units of 2e^<>h. In order to satisfy requirements for downsizing from mesoscopic scale to atomic scale in electronics, it is necessary to examine various phenomena occurring in such atom-sized systems. With this in mind, we examine the effects of the constricted structure of the atom-sized bridge and the effects of the Coulomb interaction between electrons on the quantized conductance through an atom-sized bridge. The obtained results are summarized as follows.1. The effects of the constricted structure of … More the atom-sized bridge :Stepwise variation of the conductance is disturbed by the broken symmetry of the shape of the atom-sized bridge.2. The effects of the intra-site Coulomb interaction between electrons :At finite temperatures, the Coulomb interaction causes various types of electron-electron scattering processes, inter-subband as well as intra-subband scattering processes and Umklapp as well as normal scattering processes, and strongly affects the quantum transport property of an atom-sized bridge. As a result, the following are derived.(1) At the conductance plateau, the deviation of the conductance value from multiples of the universal value of 2e2/h grows as the temperature is decreased. This temperature dependence is stronger for stronger Coulomb interactions.(2) Near the step, a valley structure appears as a function of the stretching length of the bridge. As the temperature is decreased, the valley gets narrower. The depth of the valley grows significantly, as the Coulomb interaction becomes stronger. Less