We report the magnetotransport measurements of a low-density, very low-disorder two-dimensional electron system realized in a GaAs/AlGaAs heterojunction. The diagonal magnetoresistance displays a structure near the filling factor $\nu =\frac{1}{7}$ which is interpreted as evidence for a developing fractional quantum Hall state. We therefore conclude, contrary to recent theoretical and experimental work, that the Wigner crystallization does not occur in this system for $\nu \ge \frac{1}{7}$.

• Received 10 June 1988

DOI:https://doi.org/10.1103/PhysRevLett.61.881