【作者】 王敏；

【导师】 聂一行；

【作者基本信息】 山西大学 ， 理论物理， 2018， 硕士

【摘要】 量子输运涉及到纳米级导体中平均电流和散粒噪声的测量,在传统的研究中,电荷涨落往往是在一个长的时间周期内被研究,从平均电流中无法获得电子的短时行为。为了描述介观结构中的短时物理性质,刻画单电子的动力学性质,提出了电荷转移的等待时间分布概念。本文基于紧束缚模型和散射理论分别对单量子点系统和T型双量子点系统中电子的等待时间分布进行了研究,讨论了系统参数对等待时间分布的影响。主要内容和结果如下:(1)研究了单能级量子点连接两个导线时电子的等待时间分布。当量子点能级与电极费米面对齐时,等待时间分布不依赖于偏压。当量子点能级偏离了费米面时,分布函数的峰值随着偏压的增加而增加,等待时间分布向短时方向移动。对于双通道量子点系统,零时等待时间分布不再为零,而且随着量子点能级偏离费米面,零时等待时间分布概率降低。随着温度的降低等待时间分布的极大值向长时间方向移动,而且最大分布概率略有降低,但温度的影响主要是在最大分布概率附近,对长时概率分布影响较小。(2)研究了T型双量子点系统中电子的等待时间分布。由于电子可以通过两条路径从左电极到达右电极,结果当点间耦合强度大于量子点与导线之间的耦合强度且偏压(或温度差)较低时,等待时间分布出现周期性的极小。随着点间耦合强度降低和偏压(温度差)的增加,周期性的极小逐渐消失。这是由T型双量子点系统两个量子点之间的点间耦合提供了两条输运路径造成的。更多还原

【Abstract】 Quantum transport involves the measurement of average current and shot noise in nanoscale conductors.In traditional studies,charge fluctuations are often studied over a long period of time,and the short-time behavior of electrons cannot be obtained from the average current.In order to describe the short-term physical properties in the mesoscopic structure and characterize the kinetic properties of a single electron,the concept of the waiting time distribution of the charge transfer is proposed.In this paper,based on tight-binding model and scattering theory,the waiting time distributions of electrons in single quantum dot system and T-type double quantum dot system are studied,respectively.The influence of system parameters on the distribution of waiting time is discussed.The following are the main contents and results of this article.(1)We study the electron waiting time distribution of single-level quantum dots coupled two leads.When the quantum dot energy level is aligned with the Fermi surface of the electrode,the waiting time distribution is independent of the bias voltage.When the quantum dot energy level deviates from the Fermi surface,as the bias voltage increases,the peak of distribution function increases and the waiting time distribution shifts towards shorter time.For a two-channel quantum dot system,the zero-time waiting time distribution is no longer zero and decreases as the quantum dot energy level deviates from the Fermi surface.With the temperature decreasing,the maximum value of waiting time distribution moves to a long time,and the maximum of distribution decreases slightly.However,the influence of temperature is mainly in the vicinity of the maximum distribution probability and has little effect on the long-term probability distribution.(2)We study the waiting time distribution of electrons in the T-type double quantum dot system.Since the electrons can reach the right electrode from the left electrode through two paths,when the interdot coupling is bigger than the coupling strength between the quantum dot and the wire and bias(or temperature)is lower,the waiting time distribution shows periodical minimum.With the decrease of the interdot coupling and the increase of the bias voltage(temperature difference),the periodical minimum gradually disappears.This is due to the fact that the interdot coupling between the two quantum dots of a T-type double quantum dot system provides two transport paths.更多还原