Theoretical Solid State Physics

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

TECHNICAL SUMMARY: This award supports theoretical research and education in condensed matter physics and computational materials science. The projects cover a range of topics including studies of graphene, nanotubes, semiconductors, metals, interfaces, superconductivity, magnetic systems, and molecular junctions. The major objective is to explain and predict the properties of materials. These areas are addressed using previously developed and ongoing enhancements to theoretical and computational techniques based on quantum theory. These techniques enable accurate calculations for real materials. In particular, the ab initio pseudopotential method and total energy techniques are applied within the density functional formalism to compute ground-state properties. Excited-state (spectroscopic) phenomena are investigated using a first-principle self-energy approach based on the GW approximation for quasiparticle excitations and an ab initio two-particle Green's function method based on the Bethe-Salpter equation for optical excitations. Other studies rely on molecular dynamics and Monte Carlo simulations, dielectric function methods, BCS theory, density functional perturbation theory, and extensions of standard many-body theory. Augmentation of existing methods to deal with electron correlations and localized methods are also employed. Close collaborations with various experimental groups are an essential component of this research activity. Past successes include accurate predictions of properties and the existence of new materials including nanostructures, and electronic structure calculations which allow band gap engineering approaches for technology. The present effort extends existing research and adds several projects related to understanding and predicting the properties of graphene systems, nanotubes, and related nanostructures; electronic and structural properties of semiconductors, metals, and novel materials; quasiparticle excitations, excitonic effects, and optical responses of materials and reduced-dimensional systems; electron transport through molecular and nanoscaled junctions; superconductivity, electron-phonon interactions, and related phenomena. The research, though basic, supports further development of advanced materials, especially those relevant to semiconductor technology and nanoscience. The broader impacts of the effort include the education and professional training of graduate students and postdoctoral researchers, as well as the development of computer codes that can be used by many physics and chemistry researchers and by engineers for applications. NON-TECHNICAL SUMMARY: This award supports theoretical research and education in condensed matter physics and computational materials science. The projects cover a broad range of topics including the fields of high performance materials and nanoscience. The research will contribute to the development of theoretical and computational techniques based on quantum theory to enable accurate calculations of measured properties as well as the prediction of the characteristics and the existence of new materials that were not previously created in the laboratory. These techniques have high reliability because the computations are based on theory developed from basic principles of physics. Specific projects include those related to understanding and predicting the properties of exotic materials such as graphene (a two-dimensional, single layer of carbon) and nanostructures (structures that are some 100,000 times smaller than the human hair) and semiconductors important for technology. The properties of interest include characteristics related to how materials interact with light (such as absorption and emission), material strength, and electrical properties, to name a few. The project is well suited for involving graduate students and researchers just beyond their graduate degrees, hence, it will significantly contribute to the education and training of a scientifically capable workforce. The theoretical work bears directly on experimental studies resulting in frequent experimental-theoretical collaborations on basic and applied science.