Frictional drag between parallel two-dimensional electron gases in a perpendicular magnetic field

We present measurements in a perpendicular magnetic field of the frictional drag between two closely spaced, but electrically isolated, two-dimensional electron gases. At high temperatures, when the Landau level structure is smeared out, the transresistivity shows a B-2 magnetic field dependence and an approximately linear temperature dependence. As the temperature is lowered below 20 K, the transresistivity shows structure reflecting the formation of Landau levels and, in general, the drag is more sensitive to the spin splitting of the Landau levels than the Shubnikov-de Haas oscillations. When the Fermi energy E(F) lies at the centre of a Landau level, the drag can be enhanced by two orders of magnitude over the zero field signal. In contrast, when E(F) lies between Landau levels in the quantum Hall regime, the drag signal tends to zero. We have also measured the transverse voltage in the drag layer and find no evidence for a Hall transresistance.