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Prof. Gregory Stewart

RESEARCH INTERESTS OF G. R. STEWART

Iron Pnictide Superconductors:

With the discovery of superconductivity up to Tc=57 K (fueled by the Hosono group's discovery of superconductivity at 26 K in LaFeAsO doped with F), a number of interesting physical questions have been raised.  Chief among these are:  What other compounds with perhaps even higher transition temperature can be found?  What role do non-conventional pairing mechanisms (including spin fluctuations) play in the superconductivity?

We are investigating both known, and as-yet uninvestigated compounds (there are over 800 known systems in the '1111' structure (like LaFeAsO) and the '122' structure (based on BaFe2As2)).  In addition, specific heat as a function of angle and field up to 20 Tesla and down to 0.1 K are either under investigation or being planned.

Non-Fermi-liquid behavior in d- and f-electron metals:

The Landau Fermi-liquid theory is the typical framework for the discussion of low-lying excitations in metals, which behave as a collection of weakly interacting electronlike particles. This approach describes the equilibrium and transport properties of most metals. A class of relatively complex materials has emerged, involving more than 100 systems, which is not described by Landau Fermi-liquid theory. These newly discovered materials are called, appropriately enough, non-Fermi liquids. Our group, using various theoretical insights, is actively involved is finding new non-Fermi liquid systems, as well as characterizing already known systems (click on Publications link at left.) Students in our laboratory learn to make both polycrystalline (plasma arc melting) and single crystal (metal flux method) samples, as well as characterizing the materials using our characterization techniques including x-ray diffraction, resistivity, dc and ac susceptibility, and - our speciality measurement - specific heat in fields up to 45 T at the National High Magnetic Field Laboratory in Tallahassee.

Our group is involved in a number of ongoing, active collaborations, including research groups in Goettingen, UC San Diego, Kyoto University, Missouri University of Science and Technology, CalState San Diego, Los Alamos National Laboratory,  and (starting in 2008) Seoul National University.