Effect of the Electrodynamic Environment on Electrical Transport in Nanoscale Structures

[9974365rimberg]这个项目的重点是在可调辐射源的存在下研究隧道过程。在许多纳米系统中，量子力学隧穿是电输运的一个重要过程。在凝聚态系统中，当考虑隧道效应时，不仅要注意电子（或其他粒子）本身的隧道效应，还要注意它们耦合到的电磁环境。在许多情况下，环境是固定的，没有很好地表征。在这个项目中，一个由隧道结构和可调环境耦合组成的模型系统已经被制造出来。该系统由Al/AlOx单电子晶体管（SET）耦合到GaAs/AlGaAs异质结构中的量子点组成。Al/AlOx隧道结具有高势垒和缺陷少的特点，是理想的隧道元件。量子点形成了一个非常灵活的环境，因为它的阻抗和能级结构可以在一个物理上有趣的范围内调节。随着量子点的限制程度的变化，通过测量SET的直流I-V特性，人们能够观察到环境的变化如何影响通过SET的传输。此外，由于SET I-V特性对环境的阻抗和频率eV/h（其中V为施加电压）自然敏感，因此还可以获得有关点在千兆赫频率范围内的阻抗的信息。该项目的研究也将为研究生和本科生以及博士后研究助理提供一个机会，让他们在21世纪未来几十年的重要技术领域获得最先进的实验技能。在许多非常小的物理系统（边长只有几百亿分之一米的系统）中，面对势垒的电子可以“隧穿”势垒而不是越过它。在许多微小结构中，这种过程是电传导的主要形式。电子周围的环境，包括其他电子的存在或振动，都会影响它的隧穿能力。然而，在许多情况下，不清楚环境中的什么因素在影响隧道建设，而且通常不可能改变它。本研究建议使用两种专门的设备来解决这个问题。一种是单电子晶体管，可以很好地控制隧穿；事实上，这个装置中的电子可以一次一个地穿隧。第二种装置被称为量子点，由少量（只有几百个）电子组成，这些电子被能量垒限制在一个很小的区域内。通过控制障碍的高度，就有可能控制电子进入或离开点的难易程度。这种可变性将允许网点作为一个很好理解和可调的人工环境。通过在非常靠近点的地方制造单电子晶体管，人们能够观察到点的变化如何影响晶体管中的隧道。本研究的目标是更清楚地了解极小结构中导电是如何工作的，从而指导亚纳米技术中量子结构技术实现的进一步进展。本科生和研究生以及博士后研究助理将参与本研究。因此，他们将获得最先进的技能，为21世纪科学和技术前沿领域的就业做好准备。

9974365RimbergThis project focuses on the investigation of the tunneling process in the presence of a tunable source of radiation. In many nanoscale systems, quantum mechanical tunneling is a fundamentally important process in electrical transport. In condensed matter systems, when considering tunneling attention must be paid not only to the electrons (or other particles) which are themselves tunneling, but also the electromagnetic environment to which they are coupled. In many cases the environment is fixed and not well characterized. In this project a model system consisting of a tunneling structure coupled to a tunable environment has been fabricated. The system consists of an Al/AlOx single-electron transistor (SET) coupled to a quantum dot in a GaAs/AlGaAs heterostructure. The Al/AlOx tunnel junctions form nearly ideal tunneling elements due to their high barriers and lack of defects. The quantum dot forms an extremely flexible environment, since its impedance and energy level structure are tunable over a physically interesting range. By measuring the dc I-V characteristics of the SET as the degree of confinement of the quantum dot is varied, one is able to observe how changes in the environment affect transport through the SET. Furthermore, since the SET I-V characteristics are naturally sensitive to the impedance of the environment and to frequencies eV/h where V is the applied voltage, one may also obtain information about the impedance of the dot at frequencies in the gigahertz range. The research in this project will also serve as an opportunity for students, both graduate and undergraduate, as well as post doctoral research associates to acquire state-of-the-art experimental skills in an area of great technological importance during the next few decades of the 21st Century.%%% In many very small physical systems (ones which measure only a few tens of billionths of a meter on a side), electrons facing a barrier can "tunnel" through the barrier instead of going over it. This kind of process is the dominant form of electrical conduction in many tiny structures. The environment surrounding an electron, including the presence of other electrons or of vibrations, can affect its ability to tunnel. In many cases, however, it is unclear what in the environment is affecting the tunneling, and it is usually impossible to change it. This research proposes to use two specialized devices to approach this problem. One, known as a single electron transistor, allows great control over tunneling; in fact electrons in this device can be used to tunnel one at a time. The second device, known as a quantum dot, consists of a small number (only a few hundred) of electrons confined in a very small area by energy barriers. By controlling the height of the barriers it is possible to control how easy or difficult it is for electrons to enter or leave the dot. This variability will allow the dot to serve as an artificial environment that is well understood and tunable. By fabricating the single electron transistor very close to the dot, one is able to observe how changes in the dot affect the tunneling in the transistor. The goal of this research is then to obtain a clearer understanding of how electrical conduction works in extremely small structures and thereby guide further advances in the technological realization of quantum structures in subnano-technology. Undergraduate and graduate students, as well as post doctoral research associates will participate in this research. They will thereby acquire state-of -the-art skills that will prepare them for employment in forefront areas of science and technology during the 21st Century.