Physics of Non-Fermi Liquid Metals

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TECHNICAL SUMMARYThis award supports theoretical research on heavy fermion materials with a particular focus on quantum criticality. The strongly correlated many-electron systems of interest are in regimes that are not adiabatically connected to the limit of free-electron gas, and theoretical understanding of the pertinent non-perturbative physics of electron correlations are still at a very early stage. The PI will study model systems which are amenable to controlled theoretical studies and which may provide lessons for other more complex systems. The PI will pursue four specific research directions: 1.) Quantum Transition out of Magnetic Order in Heavy Fermions: The PI will study ways in which quantum transitions can take place from magnetically-ordered heavy fermion metals. This research is motivated by recent experiments in heavy fermion metals, which suggest at least three routes for such transitions. Another motivation is to shed new light on the nature of heavy fermion quantum criticality.2.) Superconductivity in Quantum Critical Heavy Fermions: The PI will study whether and how unconventional superconductivity arises in heavy fermion metals near a Kondo-collapsing quantum critical point. This work will leverage advances of the past few years on quantum criticality beyond the Landau paradigm of order-parameter fluctuations, and will also aim to elucidate the interplay between quantum criticality and superconductivity in Ce-115 and related systems.3.) Quantum Criticality from a Gravitational Perspective: The PI will seek to gain new insights into the Kondo-collapsing local quantum criticality from a dual picture formulated in terms of gravity in an anti-de Sitter space. The PI will explore the possibility that a heavy-fermion quantum critical point contains the factorization of spatial and temporal fluctuations as an emergent symmetry.4.) Fluctuation and Dissipation of out-of-equilibrium Quantum Criticality: A quantum critical point is readily driven out of equilibrium, as its scale-invariant fluctuation spectrum implies the lack of any intrinsic energy scale. We will consider the fluctuations and dissipation of a magnetic nanostructure as a concrete setting to study the larger issues in non-equilibrium.This research project will engage postdoctoral fellows, graduate students, and undergraduate students, and will contribute to the understanding of materials that may form the foundations of future technologies.NON-TECHNICAL SUMMARYThis award supports theoretical research and education on a class of unusual materials. 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. The PI will develop new theoretical methods to study how textbook descriptions for the electronic states of metallic materials and for the transformation between electronic states can fail, and how new electronic states of matter can arise. This research project will engage postdoctoral fellows, graduate students, and undergraduate students, and will contribute to the understanding of materials that may form the foundations of future technologies.