Non Fermi Liquid Physics and Quantum Critical Phenomena

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TECHNICAL SUMMARY:This award supports theoretical and computational research and education in condensed matter physics. The research is aimed at developing and validating the concepts and the theoretical and computational methods needed to understand the physics of materials that do not obey the Landau Fermi liquid paradigm. There are 4 major components to the project: (1) The PI plans to carry out analytical and numerical calculations of model systems properties aimed at interpreting and understanding the implications of a new kind of experimental measurement; namely the "infrared/optical Hall effect," which probes the motion of electrons exposed to a static magnetic field and to an electric field alternating at infrared or optical frequencies. (2) This component focuses on "quantum criticality", the behavior occurring when the ground state of a material changes from one phase, for example paramagnetic metal, to another phase, for example antiferromagnetic metal. Materials near a quantum critical point typically exhibit large amplitude, long range, slowly changing fluctuations, which are known empirically to couple to the electrons, leading to large deviations from the predictions of fermi liquid theory. Moreover, the slow spatial and temporal variation of these fluctuations means that their effects can be studied using established techniques of quantum field theory. Analytical calculations will be performed, and compared to recent measurements on quasi two dimensional quantum antiferromagnetic transitions, with applications to high temperature superconductivity. (3) This component involves developing and validating new numerical methods for calculating the thermodynamics and dynamics of systems not adequately described by conventional methods. Considerable progress has been made in recent years based on the "dynamical mean field" approximation. New methods of solving the dynamical mean field equations have been developed and will be further improved, will be implemented for a wide range of systems, and applied. (4) The PI aims to extend our understanding of equilibrium physics into the nonequilibrium domain relevant for example for the nanoscience of molecular devices. New analytical and numerical methods will be explored for calculating the properties of systems in a steady state non-equilbrium situation.This research project will contribute to the training of young scientists who can look at problems from a broad perspective; combining fundamental insights with concrete applications.NON-TECHNICAL SUMMARY:This award supports theoretical and computational research and education in condensed matter physics. Why is the whole greater than the sum of its parts? How do simple constituents, the electrons and atoms which are the building blocks of the world around us, combine together to give amazing variety of things we see? This research project involves theoretical work designed to address these questions in one specific area of materials theory, namely the physics of "non-fermi-liquid" metals. "Fermi liquid theory", created by the Soviet physicist L. D. Landau in the late 1950s, is the reigning and widely successful intellectual paradigm for understanding the properties of electrons in metals. However, it fails conspicuously to describe for example the ability of the copper-oxide high temperature superconductor materials to carry a super-current with no electrical resistance at unprecedentedly high temperatures, the 'colossal' dependence of electrical resistance on magnetic field in manganese oxide compounds, or the changes to the conductance properties of nanoscale and "single molecule" devices. The experimental discovery of additional examples seems just around the corner. This research will contribute to the creation of new concepts and new theories, and new computational algorithms that will enable the understanding of complex materials with unusual properties that are the fuel for the discovery of new phenome and for the creation of new technologies. This research project will contribute to the training of young scientists who can look at problems from a broad perspective, combining fundamental insights with concrete applications, to tackle the future challenges of science and technology.