Spin anomalies in the magneto-drag between double layer 2DEGs

We have measured the low temperature magneto-drag between two two-dimension al electron gases (2DEGs). At matched densities, minima at odd filling fact or are observed down to fields at which the Zeeman energy is only one tenth of temperature. At mismatched densities a novel 1/B periodic oscillation i n the magneto-drag is observed with frequency h/2e time's the density misma tch between the 2DEGs. The oscillation causes negative minima when the fill ing factor difference between the 2DEGs is odd and positive maxima when it is even. An empirical model is presented that assumes a negative contributi on to the drag from electrons with anti-parallel spin in each layer and a p ositive contribution from electrons with parallel spin. The model faithfull y reproduces the experimental results at matched as well as mismatched dens ities. (C) 2001 Elsevier Science B.V. All rights reserved.