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

Abstract

We observe deep minima in the diagonal resistivity ${\rho }_{\mathrm{xx}}$ 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 ${\rho }_{\mathrm{xx}}$ as T→0 and persist up to temperatures of ∼10 K. In spite of the strength of the ${\rho }_{\mathrm{xx}}$ features, no indication of plateau development is visible in the Hall resistance ${\rho }_{\mathrm{xy}}$. These structures at half-filling appear to have their origin in a novel many-particle state distinctly different from the fractional quantum Hall effect.