This award supports theoretical research and education in condensed matter physics. The PI will focus on two complementary and intertwined subjects: the origins of non-Fermi liquid behavior and quantum criticality. On the one hand, experiments in strongly correlated materials have provided ample evidence for the failure of the conventional theory of electrons in solids, Landau's Fermi liquid theory. Understanding the mechanisms for non-Fermi liquid behavior is one of the fundamental issues with many open questions. On the other hand, a number of metallic systems have emerged as prototype materials in which quantum criticality can be systematically studied. The challenge to theory is enormous, because the critical fluctuations are both collective and quantum mechanical. Perhaps the most pressing question is whether the traditional picture based on order-parameter fluctuations is adequate, or whether inherently quantum degrees of freedom must be incorporated as part of the critical modes. These issues are important for a wide range of novel quantum materials, including heavy fermion metals, high temperature superconductors, and quantum nanostructures. The proposed research is comprised of three specific directions: 1. Global phase diagram of magnetic heavy fermions: Here the PI will pursue the notion that quantum phases in magnetic heavy fermion metals are not only characterized by conventional order parameters, but also by the nature of their Fermi surface. Both antiferromagnetic and ferromagnetic heavy fermion systems will be considered, and the implications for quantum criticality will be addressed. 2. Quantum phases in itinerant frustrated quantum magnets: The PI seeks to understand the origin of the singular heavy fermion behavior in f-electron metals with geometric frustration. 3. Nonequilibrium aspects of Quantum Criticality: The PI will study the nonlinear transport and other non-equilibrium properties of a single-electron transistor with ferromagnetic leads, which can be tuned through a quantum critical point. This project not only is of interest in the context of nanostructures, but also provides a theoretically controlled setting to explore the non-equilibriums aspects of quantum criticality. This research project will engage junior scientists as well as undergraduate students, providing them with advanced theoretical training. The research will advance the understanding of electronic materials that are potentially important for thermoelectric, magnetic information, and spintronic technologies.
NON-TECHNICAL SUMMARY: This award supports theoretical research and education in condensed matter physics. The discovery of complex metallic materials with unusual properties that lie outside the standard textbook description of metals has motivated intense research that aims to understand the physical origins of their properties. The PI will use advanced theoretical methods to attack this problem with a focus on elucidating the nature of a transformation from one state of matter to another that takes place at the absolute zero of temperature. In contrast to the familiar transformation of water to ice that takes place around 273K, or 0C, and in which temperature plays an important role, this transformation is driven by a fundamental principle of quantum mechanics ascribed to Heisenberg. The PI is developing a theory of these transformations and the unusual temperature dependent properties that they induce. This research project will engage junior scientists as well as undergraduate students, providing them with advanced theoretical training. The research will advance the understanding of electronic materials contributing to the intellectual foundations of possible new technologies, information and electronic device technologies in particular.
