We have experimentally examined the effects of periodic density modulation on correlations in a 2D electron system with tunable gate structures using dc transport and surface acoustic waves (SAW). Application of a modulation induces a dramatic transition at filling factor 1/2 where the properties of the composite fermion Fermi surface are replaced by a large effect similar to that displayed by quantum Hall states. This new effect occurs for SAW measurements orthogonal to the modulation wave vector and only for a sufficiently small modulation period. No immediate explanation is assigned to this effect.
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Willett et al. (1997) studied this question.
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