General Colloquium:
September 16 - 4:00pm Phys 223
(Coffee at 3:30p.m. in room 242)
Professor J.J. Quinn
Department of Physics and Astronomy
University of Tennessee, Knoxville
Title: "Composite Fermions and the Fractional Quantum Hall Effect"
In the presence of a magnetic field B the
energy spectrum of a two dimensional electron gas consists of
highly degenerate Landau levels. Each level can accommodate n_\phi
= B / \phi_0 electrons per unit area, where \phi_0 \equiv hc/e is
the quantum of flux. A sequence of incompressible quantum fluid
states is observed at filling factors \nu \equiv n / n_\phi which
are integers (integral QH effect) or odd denominator fractions
(fractional QH effect), where n is the elecctron concentration.
The energy gap causing the incompressibility at fractional
fillings results from electron-electron interactions. Laughlin
explained the condensed states occurring at \nu^{-1} equal to an
odd integer by correctly guessing the form of the correlations
caused by the interactions. The simplest picture for other odd
denominator fractions, the composite Fermion (CF) picture, was
proposed by Jain. What CF's are, and how the CF model works will
be discussed. The success of the CF model will be shown to depend
critically on the behavior of the pseudopotential V(L_12)
describing the interaction of a pair of Fermions as a function of
their total angular momentum L_12.