Correlated-electron phases in the very low Landau level limit near ν = 1/7

A subject of long discussion in the condensed matter community is the ground state of clean two-dimensional electron systems (2DESs) in the very low Landau level limit (ν < 1/6.5). While theory suggests a transition from a series of fractional quantum Hall states (FQHSs) to a Wigner solid at some point, the exact filling at which this occurs is still controversial. Experimental studies on this regime are still rather limited because they require 2DESs with exceptional quality. Following the recent breakthrough in ultra-high-quality GaAs 2DESs [1], we revisit this problem by systematically probing correlated-electron phases near ν = 1/7 using magnetotransport measurements. In our magnetoresistance (R_xx) data, we find deep minima developing at ν = 1/7 and 2/13 in the midst of an insulating background, strongly suggesting the existence of FQHSs flanked by Wigner solid phases at these fillings. We also evaluate the magnetic field (B) dependent activation energy (E_A) values we obtain from the relation R_xx ~ exp(E_A/2kT), where k is the Boltzmann constant and T is the temperature. Similar to the R_xx data, minima occur at fillings ν = 1/7 and 2/13 in the B vs. E_A plots, further corroborating our view. 

[1] Y. J. Chung et al., Nature Materials 20, 632 (2021).