  We investigate the effect of a uniform background magnetic field on the
chiral symmetry breaking in SU(2) Yang-Mills theory on the lattice. We observe
that the chiral condensate grows linearly with the field strength B up to
\sqrt{e B} = 3 GeV as predicted by chiral perturbation theory for full QCD. As
the temperature increases the coefficient in front of the linear term gets
smaller. In the magnetic field near-zero eigenmodes of the Dirac operator tend
to have more regular structure with larger (compared to zero-field case)
Hausdorff dimensionality. We suggest that the delocalization of near-zero
eigenmodes plays a crucial role in the enhancement of the chiral symmetry
breaking.
