Theoretical Solid State Physics

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

NONTECHNICAL SUMMARY This award supports theoretical and computational research and education with the goals of understanding the electronic, optical, and magnetic properties of materials and nanostructures at the microscopic level, predicting new materials and phenomena, and educating young scientists for research in this field. The fascinating properties and phenomena of condensed matter emerge from mutual interactions of the electrons and ions that make up materials. Understanding these interactions are central to modern technologies such as electronics, optoelectronics, photovoltaics, and energy conversion devices in general. These properties can be dramatically altered, and new phenomena can emerge, by varying the chemical composition or confining the materials to nanometer scales or exploring materials at the one- or two-dimensional level. This project is centered on using quantum theory, modeling, and simulations using analytical and computational tools to explain and predict the existence and properties of novel materials and nanostructures. New theoretical approaches and the availability of modern high-performance computers allow the team to obtain first-principles (i.e., with no empirical parameters) explanations and predictions of the behavior of materials including atomically thin materials, nanostructures, interfacial and defect phenomena, new superconductors, and photocatalytic materials. The educational component is focused on preparing students (graduate and undergraduate) and postdoctoral fellows for research and development in the current quantum technological revolution. The computational tools developed from the project will be 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. The research is grouped into three topical areas of condensed matter physics and materials science: 1) novel phases and structures of materials; 2) optical and spin physics of reduced-dimensional systems, and 3) electron-phonon coupling, light-matter interaction, and superconductivity. The major objective is to use many-body quantum theory, high-performance computing, and new concepts such as those from topology to explain and predict the properties of and phenomena in real materials, including lower dimensional systems. Several state-of-the-art approaches based on many-body quantum theory are employed to enable accurate first-principles calculations for real materials. Ground-state properties are obtained using the ab initio pseudopotential density functional theory formalism. Excited-state properties are calculated from the interacting one-particle Green's function within the GW approximation for quasiparticle excitations and the interacting two-particle Green's function via the Bethe-Salpeter equation for optical properties. Electron-phonon couplings are computed using a new methodology based on GW perturbation theory. Time-dependent phenomena under driven fields and nonlinear optical responses are computed using another newly developed time-dependent adiabatic GW method. A host of properties are shown to be accessible with the above methods. Examples include structural information, electronic structure, energy gaps, optical and photoemission spectra, electronic topological invariants, surface and interface characteristics, vibrational and mechanical properties, magnetic properties, transport properties, pump-probe spectroscopies, nonlinear optical responses, and properties of conventional superconductors. Theoretical and methodological developments are also carried out to further advance our conceptual and computational capabilities. The first-principles calculations are augmented with model Hamiltonian studies when appropriate, especially for understanding topological effects and systems with stronger electron correlations. The educational component is focused on training of students (graduate and undergraduate) and postdoctoral fellows for research and development in the current quantum technological revolution. The computational tools developed from the project will be incorporated into three open-source software packages - Berkeley GW, PARATEC, and EPW - which are freely available to the community on the web. 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.