Transport and Optical Phenomena in Correlated Electron Systems

NONTECHNICAL SUMMARYThis award theoretical research on transport and optical properties of materials with unconventional electronic behavior. Investigations of transport and optical phenomena in condensed matter systems provides invaluable information about the dynamics of electrons and how they interact with each other and atomic vibrations. However, the analysis and interpretation of abundant experimental data is never straightforward and, quite often, challenging, due to a multitude of competing processes. One encounters such challenges even when describing electron transport in simple conventional metals, such as copper and aluminum, where electrons behave as almost free particles. Analysis becomes even more complicated in materials where strong electron-electron interaction erases any similarities with the free-electron picture. In this project, the PI and his team will investigate transport and optical properties of several unconventional systems, such as those where the strong interaction leads to a linear temperature dependence of the resistivity, systems where the electron's energy depends on its momentum in a linear fashion, and materials in which the spontaneous alignment of electric dipole moments is overcome by the quantum motion of the atoms. Studying these puzzling systems is not only important for advancing our scientific understanding of materials in general, but they could also potentially lead to technological innovations in the future, such as in lossless transmission of electricity and quantum information science.This award also supports educational and outreach activities. The PI will develop new moduli on subjects relevant to this award for a multi-faculty course on Advanced Topics in Condensed Matter Physics, adopt and revamp a joint History/Physics course that offers a dual exploration of physics discoveries from scientific and historical points of view, organize various workshops and conferences, and work on a new book on Quantitative Methods in Physics aimed at upper-undergraduate and graduate students. TECHNICAL SUMMARYThis project entails theoretical research on transport and optical properties of unconventional electronic systems. The research has three main objectives. In the first thrust, the PI and his team will focus on the theory of spin collective modes in bilayer graphene with proximity-induced Rashba and valley-Zeeman types of spin-orbit coupling, which will provide a new development in the Fermi-liquid theory with multiple electron valleys, spin-momentum locking, and non-Abelian Berry curvature. The second objective is to develop a detailed theory of intrinsic optical absorption in Dirac and Weyl semi-metals, induced by electron-electron and electron-hole interactions. At the first stage of this effort, the PI’s group will study optical absorption in model systems, at the level of low-energy single-particle Hamiltonians, accompanied by both Hubbard and Coulomb interaction. Subsequently, the group will turn to more realistic, material-dependent Hamiltonians and make specific predictions for optical absorption in real materials. The third objective is to describe theoretically several puzzling phenomena observed in doped quantum paraelectrics such as strontium titanate. The topics to be addressed within this objective include (i) the origin of the quadratic-in-temperature behavior of the resistivity; (ii) a proper description of charge and heat transport in a thermal metal without quasiparticles, and beyond the Planckian limit, (iii) the origin of a strong temperature dependence of the effective mass, as measured by optics and thermoelectric effect; and (iv) the origin of quasi-linear and quasi-isotropic magnetoresistance.This award also supports educational and outreach activities. The PI will develop new moduli on subjects relevant to this award for a multi-faculty course on Advanced Topics in Condensed Matter Physics, adopt and revamp a joint History/Physics course that offers a dual exploration of physics discoveries from scientific and historical points of view, organize various workshops and conferences, and work on a new book on Quantitative Methods in Physics aimed at upper-undergraduate and graduate students.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.