COMPOSITE FERMIONS IN PERIODIC AND RANDOM ANTIDOT LATTICES

The longitudinal and Hall magnetoresistance of random and periodic arr ays of artificial scatterers, imposed on a high-mobility two-dimension al electron gas, were investigated in the vicinity of Landau level fil ling factor nu=1/2. In periodic arrays, commensurability effects betwe en the period of the antidot array and the cyclotron radius of composi te fermions are observed. In addition, the Hall resistance shows a dev iation from the anticipated linear dependence, reminiscent of quenchin g around zero magnetic field. Both effects are absent for random antid ot lattices. The relative amplitude of the geometric resonances for op posite signs of the effective magnetic field and its dependence on ill umination illustrate enhanced soft wall effects for composite fermions .