  Composite fermions (CFs), exotic particles formed by pairing an even number
of flux quanta to each electron, provide a fascinating description of phenomena
exhibited by interacting two-dimensional electrons at high magnetic fields. At
and near Landau level filling $\nu=1/2$, CFs occupy a Fermi sea and exhibit
commensurability effects when subjected to a periodic potential modulation. We
observe a pronounced asymmetry in the magnetic field positions of the
commensurability resistance minima of CFs with respect to the field at
$\nu=1/2$. This unexpected asymmetry is quantitatively consistent with the CFs'
Fermi wave vector being determined by the \textit{minority} carriers in the
lowest Landau level. Our data indicate a breaking of the particle-hole symmetry
for CFs near $\nu=1/2$.
