Physics of Non-Fermi Liquid Metals

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NONTECHNICAL SUMMARYThis award supports theoretical research and education in the many-body physics of strongly correlated electrons. For common solids such as silicon or aluminum, their electronic properties are well described by a theory that is based on an assumption of essentially independent electrons. In the recent past, an increasing number of materials have been found to contain electrons that in fact interact strongly with each other. These interactions between electrons give rise to a variety of possible ways in which the electrons can be organized in the material, and create the possibility of phase transitions. These phase transitions are the quantum analogues of familiar phase transitions such as ice melting into water. The PI will develop theoretical methods to i) study the collective behavior of electrons in such settings, ii) understand how novel electronic states can arise, such as superconductivity, in which electrons conduct electricity without experiencing any resistive loss of energy, and iii) explore what happens when the electrons are put under the influence of an external driving force, such as electromagnetic radiation. The research will provide opportunities to train graduate and undergraduate students in cutting-edge theoretical methods, including opportunities for training in an international setting through the PI's collaborations with experimentalists worldwide. The project will contribute to the understanding of modern materials that may be important for future energy and information technologies.TECHNICAL SUMMARYThis award supports theoretical research and education in the many-body physics of strongly correlated electrons. The textbook description of electrons in solids is based on a theory in which electrons only interact weakly with each other. When electron correlations are strong, new theoretical frameworks are needed. A very general effect of electron correlations is to induce transitions between distinct phases of matter at zero temperature. When such quantum phase transitions are continuous, quantum criticality develops and influences physical properties over a wide range of parameters and temperatures. Heavy-fermion systems represent a prototype case where the physics of quantum criticality can be systematically studied. The proposed research concerns the nature of quantum criticality that develops near antiferromagnetic and other types of ground states, as well as new instabilities that develop in the quantum critical regime. Four specific research directions will be pursued:i) The PI will analyze the instabilities of heavy-fermion metals near an antiferromagnetic order. A particular focus of the proposed work is to study the unconventional superconductivity that may develop when the quantum criticality is "beyond-Landau", as characterized by the notion of Kondo destruction.ii) Quantum criticality that involves quadrupolar degrees of freedom will be studied, with a goal of understanding some fascinating experiments that are emerging in several heavy-fermion systems.iii) The PI will explore quantum criticality at the border of a Kondo insulator, in order to shed light on the interplay between Kondo-singlet formation and antiferromagnetic order in a new setting.iv) The PI will address quantum criticality under an external drive. The proposed research aims to gain new insights into the physics of out-of-equilibrium quantum criticality using simplified models in low dimensions.In order to amplify the impact of the PI's theoretical research and expand the educational opportunities for graduate and undergraduate students involved in the PI's research program, the PI intends to continue existing and successful collaborations, and initiate new ones with experimental groups worldwide in this area. The proposed research, while fundamental in nature, will contribute to the understanding of modern materials that may be important for future technologies in energy and information.