Quantum Phase Transitions: Disorder, Dynamics, and Frustration

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).TECHNICAL SUMMARYThis award supports theoretical research and education on correlated quantum materials and nanostructures. These show a rich variety of novel phenomena due to the competition between quantum fluctuations, various interactions, quantum confinement and disorder. The quantum phase transitions that separate the different ground state phases in these systems play an important role for at least two reasons. On the one hand, their peculiar properties can control large parts of parameter space. On the other hand, they provide a novel perspective for understanding the entire phase diagram of a complex quantum system which is complimentary to traditional perturbative approaches.The major objective of this proposal is to explore quantum phase transitions in a variety of quantum materials, concentrating on three areas:1. Quantum phase transitions and quenched disorder: The PI will focus on disorder effects at first-order quantum phase transitions including those of the order-disorder type as well as transitions between competing ground state orders. Motivated by recent interesting experiments in cerium-palladium-ruthenium systems and nickel-vanadium systems, the PI will analyze the disordered itinerant ferromagnetic transition.2. Dynamics and transport at quantum critical points: The PI will study the transport properties at the superconductor-metal transition in ultrathin MoGe and Niobium nanowires. The PI will develop a theory of electronic transport in the magnetic Griffiths phases of metallic ferromagnets and antiferromagnets.3. Quantum phase transitions in geometrically frustrated magnets: The PI plans to investigate how the interplay between degeneracy, fluctuations and disorder leads to novel phases in geometrically frustrated quantum magnets, and he will study the quantum phase transitions between these phases.To carry out the research, the PI will use a combination of analytical techniques, including mean-field theory, perturbative and strong-disorder renormalization groups, and computer simulations, including classical and quantum Monte-Carlo methods, numerical renormalization group.Undergraduate students will be involved in the research. To help close the gap between classroom and research, the PI intends to complement his computational physics course, which has been instrumental for attracting undergraduates, with a seminar course on high-performance scientific computing aimed at bringing together the interested Missouri S&T students from various disciplines. The PI also aims to establish a series of ?Nobel Prize talks? to be given each fall after the Physics Nobel Prize has been announced. These talks will give an elementary introduction into the physics behind the prize, at a level accessible for non-science majors and high-school students. This series would help disseminate the excitement of science to a broader audience.NON-TECHNICAL SUMMARYThis award supports theoretical research and education on an important aspect of materials in which electrons interact with each other particularly strongly. These materials often exhibit many different phases such as different kinds of magnetism and superconductivity ? an electronic state of matter which exhibits no resistance to the flow of electricity. These phases may be separated by an unusual kind of phase transition which takes place at the absolute zero of temperature called a quantum phase transition. The points that separate phases can control the electronic properties of materials over a wide range of temperature. The PI will use advanced theoretical methods and computer simulations to study the effect of imperfections in the crystal lattice on these quantum critical points and the properties of the electronic states near quantum critical points that separate novel states of matter. The research will contribute to our understanding of an interesting and growing class of materials that display new electronic states of matter and new phenomena that provide the intellectual foundations for possible new electronic device technologies.Undergraduate students will be involved in the research. To help close the gap between classroom and research, the PI intends to complement his computational physics course, which has been instrumental for attracting undergraduates, with a seminar course on high-performance scientific computing aimed at bringing together the interested Missouri S&T students from various disciplines. The PI also aims to establish a series of ?Nobel Prize talks? to be given each fall after the Physics Nobel Prize has been announced. These talks will give an elementary introduction into the physics behind the prize, at a level accessible for non-science majors and high-school students. This series would help disseminate the excitement of science to a broader audience.