QUANTUM HALL-EFFECT IN COULOMB DRAG - INTERLAYER FRICTION IN STRONG MAGNETIC-FIELDS

We study the Coulomb drag between two spatially separated electron sys tems in the quantum Hall regime. At a fixed temperature, the drag is p eaked near the transitions between plateaus. The temperature dependenc e of the drag is a probe of the dynamics of the Hall system in a frequ ency and wave-vector regime inaccessible to transport measurements in a single layer. Most strikingly, in the transition regions it directly measures an exponent eta, discussed by Chalker, that is characteristi c of the fractal structure of the critical eigenstates.