Correlated states of 2D electrons near the Landau level filling $\nu =1/7$

Abstract

The ground state of two-dimensional electron systems (2DESs) at low Landau level filling factors ($\nu \lesssim 1/6$) has long been a topic of interest and controversy in condensed matter. Following the recent breakthrough in the quality of ultra-high-mobility GaAs 2DESs, we revisit this problem experimentally and investigate the impact of reduced disorder. In a GaAs 2DES sample with density $n=6.1\times 10^{10}$ /cm${}^2$ and mobility $\mu =25\times 10^6$ cm${}^2$/Vs, we find a deep minimum in the longitudinal magnetoresistance ($R_{xx}$) at $\nu =1/7$ when $T\simeq 104$ mK. There is also a clear sign of a developing minimum in the $R_{xx}$ at $\nu =2/13$. While insulating phases are still predominant when $\nu \lesssim 1/6$, these minima strongly suggest the existence of fractional quantum Hall states at filling factors that comply with the Jain sequence $\nu =p/(2mp\pm 1)$ even in the very low Landau level filling limit. The magnetic field dependent activation energies deduced from the relation $R_{xx}\propto e^{E_A/2kT}$ corroborate this view, and imply the presence of pinned Wigner solid states when $\nu \ne p/(2mp\pm 1)$. Similar results are seen in another sample with a lower density, further generalizing our observations.

6 pages, 4 figures

References in corpus (4)

• Thirty Years of Composite Fermions and Beyond
• Wavefunctionology: The Special Structure of Certain Fractional Quantum Hall Wavefunctions
• Spatial Mapping of Local Density Variations in Two-dimensional Electron Systems Using Scanning Photoluminescence
• Quantum bubble defects in the lowest Landau level crystal