Electron Diffraction from a 2D Electron Wigner Crystal

We describe measurements of electron diffraction by a magnetic-field-induced Wigner crystal formed at a GaAs heterojunction. The crystal is formed by dopant electrons in the lowest subband of the confining potential at the interface and is pinned by defects: the probe electrons are photoexcited into higher subbands. The signature of the electron crystal is the break-up of the density of states of the probe electron into Hofstadter bands which is detected directly in the luminescence spectrum. The measured value of the principal gap agrees well with theoretical estimates.