As a manifestation of quantum mechanics on a macroscopic scale, superconductivity is a fascinating and often counterintuitive phenomenon. Forty years after the Bardeen-Cooper-Schrieffer (BCS) theory explained the basis of superconductivity, many open questions remain. Several recently discovered classes of superconductors, such as high-Tc oxides, heavy fermion compounds, and organic superconductors, are poorly described by the standard theory. In addition, some of the more complicated behavior of BCS superconductors has never been adequately explained. As experiments achieve lower temperatures, cleaner samples, and new geometries, they highlight the gaps in understanding.

One problem I am particularly interested in is the behavior of superconductors in a magnetic field. A field penetrates a superconductor only in the form of quantized packets of flux, known as vortices. The behavior of these vortices depends on vortex-vortex interactions, randomness, crystal impurities and grain size, temperature, and dimensionality. Vortex motion is of practical as well as academic interest, since it governs the maximum current a superconducting magnet can carry with zero resistance, and the amount of dissipation at higher current. I plan to use nanofabrication techniques to make simplified systems in which the many influences on vortices can be disentangled.

I am also working on heavy fermion superconductors. These display unprecedented behavior including magnetism coexisting with superconductivity, phase transitions within the superconducting regime, and superconducting electrons with extremely large effective mass. My goals are to determine the nature of the phase transitions, to identify the superconducting order parameter(s), and to explore any new vortex structures which could result from non-s-wave order parameters.

My work involves specific heat, transport, magnetization, susceptibility, and magnetic resonance measurements. Cryogenic temperatures are reached with a 3He refrigerator or a dilution refrigerator. Certain projects also require photolithography, thermal evaporation, and other fabrication techniques.

E-mail zieve@physics.ucdavis.edu

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