Quantum Coherence and Mesoscopic Physics

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This condensed matter physics project deals with "mesoscopic" metallic samples - i.e. samples with submicron dimensions. These material can display surprising behavior, particularly in hybrid samples containing different types of materials - normal metals, superconductors, and ferromagnets. Recent theoretical predictions challenge our understanding of these materials; contradicting the long-held view that ferromagnets can not sustain superconducting correlations over distances longer than a few nanometers. This experimental project will test that prediction and others concerning electrical transport across superconductor/ferromagnet and superconductor/normal metal interfaces. In addition, experiments will probe the transport properties of normal metals when both disorder and electron-electron interactions are very strong - a regime poorly understood theoretically. Experimental research in mesoscopic physics plays an important role in educating the next generation of scientists. Graduate students involved in this project acquire expertise in modern nanofabrication techniques used in the semiconductor industry, which are also crucial to the future development and applications of nanosciences. The students are trained for careers in industry, academia, and government.When metallic samples are fabricated with very small dimensions - in the range of a micrometer - they exhibit many electrical properties not observed in larger samples. Some of the novel properties are evident at room temperature, while others are revealed only at low temperature, when electrons preserve quantum-mechanical phase coherence over many micrometers. The study of small metallic samples, called "mesoscopic physics", is a rich discipline and has led to a deeper understanding of many aspects of solid-state physics. This project addresses several current problems in mesoscopic physics, including the role of electron-electron interactions in highly-disordered metals, the complex interplay between ferromagnetic and superconducting metals in contact with each other, and the unusual behavior of superconducting/normal metal Josephson junctions driven far from equilibrium. Experimental research in mesoscopic physics plays an important role in educating the next generation of scientists. Graduate students working on these projects acquire expertise in sample processing techniques used in the microelectronics industry. The physical principles and experimental techniques developed in this kind of work are crucial to the future development and applications of nanosciences. The students and post-doctoral researchers are well trained for careers in industry, academia, and government.