Theoretical Solid State Physics

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

Nontechnical Summary This award supports theoretical and computational research and education towards understanding the electronic, optical, and magnetic properties of materials and nanostructures at the microscopic level. 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, photovoltaics, and other energy conversion devices. These properties can often be dramatically altered or new phenomena emerge from varying the chemical composition or confining the materials to nanometer scales along one or more dimensions. This project is centered on using quantum theory, modeling, and simulations to explain and predict the existence and properties of novel materials and nanostructures. New theoretical approaches and the availability of modern high performance (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 (along one or more dimensions) materials, nanostructures, interfacial and defect phenomena, new superconductors, and photocatalytic materials. The educational components are focused on training of students (graduate and undergraduate) and postdoctoral fellows for research and development in using materials in the current quantum 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, 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 by the PI and co-PI. Technical Summary This award supports theoretical and computational research and education towards understanding the electronic, transport, optical, and magnetic properties of materials and nanostructures at the microscopic level by performing first-principles quantum calculations. Topics investigated include: i) structural and dynamical properties of atomically thin one- and two-dimensional systems; ii) novel optical, topological, and magnetic properties in reduced dimensional systems and bulk materials; and iii) electron-phonon interactions, superconductivity, and associated phenomena. The major objective is to use many-body quantum theory and new concepts such as those from topology to explain and predict the properties of real materials, in particular for lower dimensional systems. Emphasis is placed on realistic models, close collaborations with experimentalists, investigations and suggestions for producing novel and useful materials, development of new theoretical and computational approaches, and predictions related to structural, electronic, magnetic, superconducting, transport and optical properties. State-of-the-art techniques based on many-body quantum theory are used to enable accurate first-principles calculations for real materials. In particular, the ab initio pseudopotential method and total energy techniques are applied within the density functional formalism (DFT) 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-Salpeter equation for optical excitations. Studies of magnetic behaviors and electron-phonon coupling phenomena, going beyond the current state of the art, are carried out using the team's newly developed renormalized spin wave method and the GW perturbation theory method, respectively. Other studies rely on molecular dynamics or Monte Carlo simulations, BCS theory, and extensions of standard many-body theory. The first-principles calculations are augmented with model Hamiltonian studies when appropriate, especially for understanding topological effects and systems with strong electron correlations. The educational components are focused on training of students (graduate and undergraduate) and postdoctoral fellows for research and development in using materials in the current quantum 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 by the PI and co-PI. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.