  Pinning of magnetic-field induced Wigner molecules (WMs) confined in
parabolic two-dimensional quantum dots by a charged defect is studied by an
exact diagonalization approach. We found a re-entrant pinning of the WMs as
function of the magnetic field, a magnetic field induced re-orientation of the
WMs and a qualitatively different pinning behaviour in the presence of a
positive and negative Coulomb impurity.
