Direct observation of micron-scale ordered structure in a two-dimensional electron system

We have extended the subsurface charge accumulation imaging method to directly resolve the interior structure of a GaAs/AlGaAs two-dimensional electron system in a tunneling geometry. We find that the application of a perpendicular magnetic field can induce surprising density modulations that are not static as a function of the field. Near six and four filled Landau levels, stripelike structures emerge with a characteristic length scale ∼2 μm. Present theories do not account for ordered density modulations on this scale.