Effect of the Electrodynamic Environment on Electrical Transport in Nanoscale Structures

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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.