Experimental evidence for new particles in the fractional quantum Hall effect

We have determined the energy gaps of both prominent sequences of fractional quantum Hall effect of (FQHE) states at filling factor ν=p/(2p±1) around ν=1/2. The gaps increase linearly with ΔB, 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 ${\mathit{m}}^{\mathrm{*}}$, and lifetime broadening Γ exposed to an effective magnetic field ΔB. 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.