Transport anomalies in the lowest Landau level of two-dimensional electrons at half-filling

We observe deep minima in the diagonal resistivity ρₓₓ of a two-dimensional electron system in GaAs at Landau-level filling factor {ν}=(1/2 and (3/2. The anomalies saturate at nonzero values of ρₓₓ as T{→}0 and persist up to temperatures of {~}10 K. In spite of the strength of the ρₓₓ features, no indication of plateau development is visible in the Hall resistance ρxy. These structures at half-filling appear to have their origin in a novel many-particle state distinctly different from the fractional quantum Hall effect.