  Magnetic barriers in two-dimensional electron gases are shifted in B space by
homogeneous, perpendicular magnetic fields. The magnetoresistance across the
barrier shows a characteristic asymmetric dip in the regime where the polarity
of the homogeneous magnetic field is opposite to that one of the magnetic
barrier. The measurements are in quantitative agreement with semiclassical
simulations, which reveal that the magnetoresistance originates from the
interplay of snake orbits with E x B drift at the edges of the Hall bar and
with elastic scattering.
