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Prof. Gregory Stewart

RESEARCH INTERESTS OF G. R. STEWART

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.

Heavy Fermion Systems, Including Ce-, Yb-, and U-compounds:

The term ‘heavy fermion’ denotes a metallic system where, due to extremely narrow effective band widths, some of the electrons in the lattice have quite high effective masses, m^* - sometimes as much as 1000 times the electron’s mass. Much of the interest in this field remains in trying to understand the unusual superconductivity (see web page of Prof. P. Hirschfeld at http://www.phys.ufl.edu/~pjh/ for a theorist’s view). We continue to try to better understand heavy fermion superconductivity and the normal state high effective mass ground state.  Our latest project is to try to understand the response of the large m* to entry into the nano-sized regime.   We are involved in preparing and characterizing a number of new Yb compounds using single crystal metal-flux-growth techniques.

Our group is involved in a number of ongoing, active collaborations, including research groups in Goettingen, PSI Switzerland, UC San Diego, CalState San Diego, Los Alamos National Laboratory, Boston University, UC Riverside, and recently Seoul National University.