Theoretical Solid State Physics

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

Nontechnical Description: This project supports theoretical and computational research and education on condensed matter physics and materials science. The fascinating properties and phenomena of condensed matter emerge from mutual interactions of the electrons and ions that constitute the material, many of which are central to modern technologies such as electronics, optoelectronics, and energy conversion devices. Often these properties are dramatically altered or new phenomena emerge from varying the chemical composition or confining the materials to nanometer scales. This project is centered on using quantum theory, modeling, and simulations to explain and predict novel materials and nanostructures. New theoretical approaches and the availability of modern massively parallel computers allow the team to obtain first-principles (i.e., with no empirical parameters) explanations and predictions of the behavior of atomically thin materials, nanostructures, interfacial and defect phenomena, new superconductors, and photocatalytic materials. The educational components are focused on training of graduate students and postdoctoral fellows for research and development in using materials in the current technological revolution. The research findings are published in scientific journals as well as presented on the team's website. The computational tools developed from the project are incorporated into several software packages - Berkeley GW, PARATEC, and EPW - which are made freely available on the web to the research community. Another educational activity is related to public education, which is done through articles and interviews published in lay media and via public lectures. Technical Description: This project aims at understanding the electronic and optical properties of materials and nanostructures at the microscopic level by performing first-principles quantum calculations. Topics investigated include: two-dimensional (2D) crystals such as graphene and transition metal dichalcogenides; nanotubes and nanoribbons; electronic properties and photophysics of novel bulk (such as topological insulators) and reduced-dimensional systems; and superconductivity. Emphasis is placed on using realistic models, close collaborations with experimentalists, investigations and predictions of novel and useful materials, and development of new theoretical and computational approaches. Several different approaches are employed. 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 interacting two-particle Green's function method based on the Bethe-Salpeter equation for optical excitations. Other studies rely on molecular dynamics and Monte Carlo simulations, dielectric function methods, BCS theory, and extensions of standard many-body theory. Augmentation of existing methods to deal with strong electron correlations is also employed.