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Friday, September 19

New Route to a Non-Fermi Liquid

John F. DiTusa, Louisiana State University, Baton Rouge
Spallation Neutron Source Seminar
11:00 AM, Central Laboratory and Office Building (8600),
Iran Thomas Auditorium (Room A-103)
Contact: Steve Nagler (naglerse@ornl.gov), 865.574.5240

Abstract

Landau Fermi liquid theory, with its pivotal assertion that electrons in metals can be simply understood as independent particles with effective masses, has been astonishingly successful. This is true despite the Coulomb interactions an electron experiences from the host crystal lattice, its defects and the other ~1022/cm3 electrons. In the mid 1980's, an important extension to this theory was discovered by Al'tshuler to account for the behavior of doped semiconductors near metal-to-insulator transitions. There has been little in the vast literature on electrical properties of materials from macroscopic to nanometer scales that is not understood within the context of Landau Fermi Liquid theory and its extensions. This is why exceptions have attracted so much attention, and they include – most notably - the copper-oxide based high temperature superconductors, silicon-based field effect transistors which host two-dimensional metals, and certain rare earth compounds at the threshold of magnetism. The origin of the non-Fermi liquid behavior in all of these systems remains controversial. In this seminar I will present evidence that an entirely different and exceedingly simple class of materials – doped small gap semiconductors near a metal-insulator transition - can also display behavior in disagreement with conventional ideas. Remarkably, the disordered Fermi liquid can be restored by the application of a modest magnetic field. Our data suggest that we have finally found a physical realization of what is the only mathematically rigorous route to non-Fermi liquid behavior, namely the ‘undercompensated Kondo effect', where there are too few mobile electrons to compensate for the spins of unpaired electrons localized on impurity atoms1.

1N. Manyala, J.F. DiTusa, G. Aeppli, & A.P. Ramirez Nature 454, 976 (2008).