Correlated States of 2D Electrons near the Landau Level Filling v=1/7

The ground state of two-dimensional electron systems (2DESs) at low Landau level filling factors (v less than or similar to 1/6) has long been a topic of interest and controversy in condensed matter. Following the recent breakthrough in the quality of ultrahigh-mobility GaAs 2DESs, we revisit this problem experimentally and investigate the impact of reduced disorder. In a GaAs 2DES sample with density n = 6.1 x 10(10)/cm(2) and mobility is mu = 25 x 10(6) cm(2)/V s, we find a deep minimum in the longitudinal magnetoresistance (R-xx) at v = 1/7 when T similar or equal to 104 mK. There is also a clear sign of a developing minimum in R-xx at v = 2/13. While insulating phases are still predominant when v less than or similar to 1/6, these minima strongly suggest the existence of fractional quantum Hall states at filling factors that comply with the Jain sequence v = p/(2mp +/- 1) even in the very low Landau level filling limit. The magnetic-field-dependent activation energies deduced from the relation R-xx proportional to e(EA/2kT) corroborate this view and imply the presence of pinned Wigner solid states when v not equal p/(2mp +/- 1). Similar results are seen in another sample with a lower density, further generalizing our observations.

Automated summary

This study investigates the ground state of two-dimensional electron systems (2DESs) at low Landau level filling factors using improved experimental methods. It confirms the existence of fractional quantum Hall states that comply with the Jain sequence even in the extremely low Landau level filling limit.