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

• Published in: Physical review letters 2022-01, Vol.128 (2), p.026802-026802, Article 026802
• Main Authors: Chung, Yoon Jang, Graf, D, Engel, L W, Rosales, K A Villegas, Madathil, P T, Baldwin, K W, West, K W, Pfeiffer, L N, Shayegan, M
• Format: Article
• Language: English
• Subjects: CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; composite fermions; dilution refrigerator; fractional quantum Hall effect; Landau levels; Physics; two-dimensional electron gas; Wigner crystal
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.128.026802

The ground state of two-dimensional electron systems (2DESs) at low Landau level filling factors (ν≲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=6.1×10^{10}/cm^{2} and mobility μ=25×10^{6}  cm^{2}/V s, we find a deep minimum in the longitudinal magnetoresistance (R_{xx}) at ν=1/7 when T≃104  mK. There is also a clear sign of a developing minimum in R_{xx} at ν=2/13. While insulating phases are still predominant when ν≲1/6, these minima strongly suggest the existence of fractional quantum Hall states at filling factors that comply with the Jain sequence ν=p/(2mp±1) even in the very low Landau level filling limit. The magnetic-field-dependent activation energies deduced from the relation R_{xx}∝e^{E_{A}/2kT} corroborate this view and imply the presence of pinned Wigner solid states when ν≠p/(2mp±1). Similar results are seen in another sample with a lower density, further generalizing our observations.