****Technical Abstract**** In the course of this project, solid state magnetic resonance techniques will be employed to address questions related to novel magnetic field-induced phases. The systems to be studied are selected molecular superconductors and insulators with non-magnetic ground states, each exhibiting field-induced phases or phenomena with unexplored and unknown properties. These include high-field phases in layered superconductors, in a charge density wave/Spin-Peierls coupled system, and field-induced phenomena or phases in a candidate spin-liquid system. Identification of new forms of order, sometimes expected and long-sought for is the primary aim of the project, and the problems and systems are chosen accordingly. In a related effort, an association between charge ordering and frustration will be explored, with the goal of identifying a pathway to new spin liquid materials using pressure as the tuning parameter. The properties of the molecular crystals chosen for these studies are uniquely applicable to the problems addressed. Signatures for phase transitions will be looked for in the results of NMR spectroscopy and relaxation experiments, and complimentary physical properties measurements will be undertaken as appropriate. Magnetic resonance is often an ideal probe for these problems, because of its compatibility to the required extreme conditions, and because it is a local probe sensitive to the electronic environment through the hyperfine coupling. When possible, the research will be conducted in our laboratory at UCLA, and at the National High Magnetic Field Laboratory (NHMFL) for work requiring higher magnetic fields. The project will support efforts carried out by graduate and undergraduate students alike, who will be well-prepared for further work in academic or industrial laboratories.

Nontechnical Abstract

The primary aim of this project is the creation and investigation of novel phases of matter produced under extreme conditions, such as high magnetic fields, low temperatures, and high pressures. The specific problems and systems are chosen because of remarkable physical properties that tend to emerge from systems with strong electron-electron interactions and in low-dimensional systems. One such example we will be investigating is the stabilization of novel superconducting phases by high magnetic fields. Varying the non-thermal parameters (magnetic fields and pressure) allow for a continuous tuning of the important interactions, which sometimes leads to emergent properties and phases, as well as providing the conditions under which the material can be studied. Much of the work will be carried using the methods of solid state nuclear magnetic resonance (NMR) at our laboratory at UCLA and at the National High Magnetic Field Laboratory. NMR methods are locally sensitive to the electronic environment at the site of the nucleus under study. Both graduate and undergraduate students will carry out much of the experimental program, and in so doing will develop expertise in cryogenics, high-pressure techniques, and high-power radiofrequency methods, as well as a comprehensive knowledge of materials. Each will be well-prepared for further work in materials-related research or engineering laboratories.

Project Report

The project's research involved the use of magnetic resonance for the purpose of studying field-induced phase transitions and phases in quantum materials, including organic and inorganic superconductors, and magnetic systems where a form of competing interactions referred to as frustration tends to suppress magnetic order in favor of quantum fluctuations. The magnetic resonance techniques are extended to very low temperatures and very high magnetic fields as necessary. Our findings include the identification of a novel high-field superconducting phase, demonstrating the existence of a state of matter predicted nearly 50 years ago but not previously seen. The confirmation in a second material further highlights what properties are generic and not material specific. Stabilizing superconductivity at high fields remains an important goal of research in this area. In the experiments dedicated to quantum magnets, particular attention was focused on systems where the interacting spins decorated the lattice points arranged in a triangular pattern. A sequence of field-induced phases were observed, identified, and compared to a theoretical model. The phases included novel situations where quantum fluctuations have the effect of stabilizing an ordered phase. The work fits into a larger field of exploration targeting what could be called quantum disordered phases, which could find applications in quantum computers. The experiments were carried out by a team including the PI, senior collaborators, graduate students, and undergraduate students. The students were trained in areas such as cryogenic instrument design and development, radiofrequency applications at low and high power, measurement analysis and simulation, instrument control software development, as well as in quantum materials. Once graduating, the undergraduate students have moved on to graduate study in physics or engineering. The graduate students involved moved on to research- or clinic-related work.

National Science Foundation (NSF)
Division of Materials Research (DMR)
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Guebre X. Tessema
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University of California Los Angeles
Los Angeles
United States
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