Dynamical Effects in Mesoscale Electronic Systems

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This research is an experimental study of dynamic mesoscopic transport phenomena in semiconductor microstructures and hybrid metals/superconductor systems. The unifying theme is the interplay between three elements: quantum coherence, disorder or chaos, and dynamics in the form of a time-dependent potential. The proposed experiments also have in common the theme of dc pumping of charge using cyclic oscillating potentials, extending recent work on adiabatic quantum pumping to include the role of decoherence, dissipation, and nonadiabatic time dependence. Besides shape-deformable quantum dots, two novel pumping devices are proposed: a pump that operates in the fractional quantum Hall regime, allowing a pumping of fractionally charged quasiparticles, and a hybrid metal-superconductor that uses the ac Josephson effect to produce a cycling time evolution of boundary conditions. This research will be carried out in a new laboratory at Harvard University. The project will support a graduate student as well as materials and supplies needed for the experiments. Other students on these projects will be supported by independent fellowships. The students will be trained in state-of-the-art nanoelectronics techniques and will be well prepared for careers in academe, industry or government. %%%Trends in microelectronics have two clear directions, smaller and faster. The study of quantum mechanical effects in electronic devices-particularly disorder or chaotic systems-is known as mesoscopic physics, where "meso" indicates intermediate in size between atoms (where quantum physics is well understood) and the realm of large, classical electronics, governed by Ohm's law and other familiar classical laws. Mesoscopic physics has seen rapid development in the last decade, predominantly as a result of advances in the fabrication of clean semiconductors devices. By comparison, little work has been done on the high-speed side, and most of what is known about quantum-coherent devices is restricted to dc. The proposed experimental work aims to investigate quantum coherent electronic devices fabricated from semiconductors and hybrid metal/superconductor devices, at high frequencies, when effects of time evolution can lead to the destruction of quantum coherence effects, but can also lead to new effects such as the pumping of electrons due to cyclic, periodic changes in the effective shape of the device. These results will impact our understanding and development of high-speed nanoelectronics. The project will support one graduate student as well as provide materials and supplies for the project. Other students working on these experiments will have outside funding from the NSF and other sources. The students will be trained in state-of-the-art nanoelectronics techniques and will be well prepared for careers in academe, industry or government.