Carrier, Phonon and THz Dynamics in Narrow Gap and Carbon Based Nanostructures

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TECHNICAL SUMMARYThis award supports integrated research, education and outreach activities in theoretical condensed matter physics. The goal of this project is to study and model: 1) carrier-carrier, 2) carrier-phonon and 3) carrier-photon interactions in narrow gap compound semiconductor heterostructures such as indium antimonide/aluminum indium antimonide quantum wells and carbon based nanostructures. These materials are promising for our next generation of high speed transistors and detectors. Although seemingly very different, they share common features, 1) an energy-wavevector relationship that is linear for large wavevector, and 2) high room temperature mobilities. This project involves calculating and modeling the time-dependent optical and transport properties of semiconductor nanostructures. Foci include:1.) Single-walled carbon nanotubes and graphene. While the unusual DC transport properties of these materials have been previously studied, their dynamical properties are proving to be equally interesting. Coherent phonons in carbon nanotubes, graphene and graphene nanoribbons will be modeled.2.) Narrow gap InSb heterostructures. With their small effective masses and large g-factors, these materials are excellent candidates for fast transistors or novel spintronic devices. The time-dependent optical properties of these materials will be calculated and modeled to gain information about the electronic and magnetic states and transport properties. Close coupling between theory and experiment will provide an understanding of the carrier, spin, and phonon dynamics.Graduate students on this project will be trained in forefront research topics in the nanosciences including the fields of semiconductor physics, quantum optics, nanotube and nanoribbon physics, and transport theory. The students will get a chance to participate and interact with researchers both in the U.S. and also internationally. Results of their work will help determine which materials are optimal for future high speed nano-electronic devices and detectors. NON-TECHNICAL SUMMARYThis award integrates research, education and outreach in theoretical condensed matter physics. The motivation of the project is to study and understand properties of two new classes of nanostructured materials that are promising materials for the next generation of high speed transistors, and optical sources and detectors. These materials are: 1.) structures made of carbon that resemble ribbons or tubes of nanoscale dimensions - some ten thousand times smaller than the width of a human hair - called carbon nanotubes and carbon nanoribbons, 2.) graphene which is a single layer of carbon atoms which resembles chickenwire on the nanoscale with carbon atoms arranged at the vertices, and 3.) nanoscale structures made of a compound composed of elements indium and antimony, called indium antimonide.While these materials at first seem may seem very different, they share several common properties. In particular, their electronic properties are very similar and at room temperature, electrons in graphene and indium antimonide nanostructures can move faster and more easily than electrons in almost any other material including silicon and gallium arsenide. This offers hope that transistors based on these two materials may one day replace transistors based on silicon technology, currently used in today's computers. The PI will investigate how electrons in carbon and indium antimonide nanostructures interact and scatter with 1.) other electrons, 2.) atoms that are moving in the nanostructures and 3.) electromagnetic radiation. The interaction with electromagnetic radiation is particularly intriguing since results suggest that these materials might be used to generate and detect electromagnetic radiation in the tera Hertz part of the spectrum which lies between microwaves and infrared light. Tera Hertz radiation is non-ionizing; one day sources of this radiation may replace X-rays in medical imaging with fewer harmful side effects.Graduate students on this project will be trained in forefront research topics in the nanosciences including the fields of semiconductor physics, quantum optics, nanotube and nanoribbon physics, and transport theory. The students will get a chance to participate and interact with researchers both in the U.S. and also internationally. Results of their work will help determine which materials are optimal for future high speed nano-electronic devices and detectors.