  We study the Ginzburg-Landau energy of superconductors with a term $a_\ep$
modelling the pinning of vortices by impurities in the limit of a large
Ginzburg-Landau parameter $\kappa=1/\ep$. The function $a_\ep$ is oscillating
between 1/2 and 1 with a scale which may tend to 0 as $\kappa$ tends to
infinity.
  Our aim is to understand that in the large $\kappa$ limit, stable
configurations should correspond to vortices pinned at the minimum of $a_\ep$
and to derive the limiting homogenized free-boundary problem which arises for
the magnetic field in replacement of the London equation.
  The method and techniques that we use are inspired from those of
Sandier-Serfaty (in which the case $a_\ep \equiv 1$ was treated) and based on
energy estimates, convergence of measures and construction of approximate
solutions. Because of the term $a_\ep(x)$ in the equations, we also need
homogenization theory to describe the fact that the impurities, hence the
vortices, form a homogenized medium in the material.
