Quantum Transport in Ballistic Nanostructures

Cornell University, Ithaca NY

Investigators

Abstract

TECHNICAL SUMMARY: This award supports theoretical research and education in the area of electronic transport on nanoscale length scales. Theoretical issues connected with quantum coherent transport will be addressed to resolve several outstanding theoretical questions and experimental results that remain unexplained. Two research areas will be engaged. The first thrust addresses the physics that limits quantum interference: scattering from time-dependent potentials and fields. In disordered metal wires, the theory of phase breaking is established, but much work is needed in quantum dots and ferromagnets. The PI aims to develop a microscopic theory of phase breaking in a 'double quantum dot', in which all parameters that govern the strength of the phase-breaking rate can be accessed. In ferromagnetic conductors, experiment suggests that the phase-breaking rates in 'strong' (elemental) ferromagnets are much larger than in normal metals, although the mechanism for this enhancement is unclear. Some candidate mechanisms, for example fluctuating domain walls, magnons, and impurities, have been explored, but the picture is incomplete and will be investigated further. The second thrust deals with the quantum interference corrections themselves. The research advances the theory in ballistic conductors. In addition, the research addresses the question of how and when quantum interference corrections depend on whether the microscopic motion is ballistic or quantum-disordered. A goal of this research is to extend the theory, and to look at quantum corrections that involve interference as well as electron-electron interactions. NON-TECHNICAL SUMMARY: This award supports theoretical research and education on size effects and alterations of materials properties at the nanoscale, with an aim to enhancing our ability to make predictions and characterizations for current carrying nanostructures and nanodevices. As nanotechnology progresses to even smaller device components, the movement of electric charge through the circuits becomes less like traditional electronics and the behavior must be described in terms of quantum mechanics. The wave description of electric current includes scattering and interference and the influence of other electrons. The PI will work on the quantum theory of electrons that flow in devices that are smaller than a millionth of an inch in size. The geometries of nanodevices make this complex and the interaction of waves in nearby device components is not well understood and so is a main aspect of this research. Advances in this are required if we are ever to actually reach a miniaturization of electronics to the size of a few hundred or so atoms. Engaging students, graduate and undergraduate, in the theoretical physics behind such leading edge technology is both enlightening for undergraduates and an excellent career starting point for dissertation student. This award contributes to the effort to keep America competitive both through contributing to the intellectual foundations of future technologies and to the training of globally competitive workforce.