VELOCITY SHIFT OF SURFACE ACOUSTIC-WAVES DUE TO INTERACTION WITH COMPOSITE FERMIONS IN A MODULATED STRUCTURE

We stud!, the effect of a periodic density modulation on surface acous tic wave (SAW) propagation along a 2D electron gas near Landau level f illing nu = 1/2. Within the composite fermion theory, the problem is d escribed in terms of fermions subject to a spatially modulated magneti c field and scattered hv a random magnetic field. We find that a few p ercent modulation induces a large peak in the SAW velocity shift, as o bserved recently by Willett et al. As further support of this theory w e find the de resistivity to be in good agreement with recent data of Smet et al.