Acquisition of a High Frequency Measurement System for Mesoscopic Samples

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9625550 Webb The goal of this project is to elucidate the high frequency properties of mesoscopic structures using a state-of-the-art high frequency low noise measurement system. During the last decade it was discovered that a wave mechanics approach must be adopted when describing the propagation of an electron through any small conductor, including insulators and dirty metals as well as nearly perfect crystals. Electron interference effects, which are responsible for many of the large fluctuations observed in transport experiments, can be traced to the existence of large phase coherence times for the wave function of the electron. These large times in turn have lead to the discovery of persistent currents in normal metals, Universal Conductance Fluctuations (UCF), h/e & h2e Aharonov-Bohm effects, non-local quantum effects, length-independent conductance fluctuations, and an understanding of how these new quantum effects ensemble average to their classical values. Very little is known about the properties of the wavefunction which describes systems on time scales comparable to the coherence time (t~10-9 sec). The recent discovery that it is possible to make two terminal mesoscopic devices through which we can control the passage of electrons, one at a time, by using a third capacitively coupled gate electrode to the sample has generated much hope that these devices might be the transistors of the future. The frequency at which these single electrons pass through the device is f=IDc/e and is on the order of lx109 Hz for most samples studied to date. The applications of such a technology are quite extensive. They range from transistors to ultra-sensitive electrometers and current standards. In this project we will systematically explore the high frequency properties of these types of mesoscopic systems by using a new instrument that will allow us to directly measure the high frequency transport and magnetic properties of our samples. We believe that attemp ts to probe mesoscopic systems on a time scale comparable to the coherence time of the wavefunction will almost certainly produce a better understanding of the true nature of the quantum physics of these systems. %%% Since the physics of small structures provides the foundation upon which future electronic industry technologies may be based, it is extremely important that we identify and understand all the potentially relevant physical properties that these systems exhibit. Only after these properties are reasonably well understood can we attempt to propose to use any one of them in a new or improved technology. The work described here is a relatively new direction for the studies of mesoscopic structures: we believe experiments in the area of magnetic and transport properties of mesoscopic structures are likely to discover new phenomena which have yet to be anticipated and expand our fundamental knowledge of condensed matter science. ***