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We have determined the energy gaps of both prominent sequences of fractional quantum Hall effect of (FQHE) states at filling factor =p/ (2p1) around =1/2. The gaps increase linearly with, the deviation of the magnetic field from half filling. Therefore, the data are indistinguishable from Shubnikov--de Haas oscillations of particles of charge e, effective mass m^*, and lifetime broadening exposed to an effective magnetic field. Our findings are remarkably consistent with recent proposals of composite particles in the FQHE and the existence of a Fermi surface at even-denominator fillings.
Du et al. (Mon,) studied this question.