  Spatially resolved photoluminescence of modulation doped AlGaAs/GaAs
heterojunction was investigated in a sample of Corbino disk geometry subject to
strong perpendicular magnetic fields. Significant spatial modulation of the
photoluminescence was observed in form of one or more concentric rings which
travelled across the sample when the magnetic field strength was varied. A
topology of the observed structure excludes the possibility of being a trace of
an external current. The effect is attributed to formation of compressible and
incompressible stripes in a 2DEG density gradient across the sample.
