Marginal metallic state at a fractional filling of '8/5' and '4/3' of Landau levels in the GaAs/AlGaAs 2D electron system

A metallic state with a vanishing activation gap, at a filling factor ν = 8/5 in the untilted specimen with n= 2 x 10¹¹ cm^-2, and at ν = 4/3 at n=1.2 x 10¹¹ cm^-2 under a θ = 66⁰ tilted magnetic field, is examined through a microwave photo-excited transport study of the GaAs/AlGaAs 2 dimensional electron system (2DES). The results presented here suggest, remarkably, that at the possible degeneracy point of states with different spin polarization, where the 8/5 or 4/3 FQHE vanish, there occurs a peculiar marginal metallic state that differs qualitatively from a quantum Hall insulating state and the usual quantum Hall metallic state. Such a marginal metallic state occurs most prominently at ν=8/5, and at ν=4/3 under tilt as mentioned above, over the interval 1 ≤ν≤ 2, that also includes ν= 3/2, which appears perceptibly gapped in the first instance.[1]

[1] Mani, R.G., Wijewardena, U.K., Nanayakkara, T.R., Kriisa, A., Reichl, C., and Wegscheider, W. Marginal metallic state at a fractional filling of ’8/5’ and ’4/3’ of Landau levels in the GaAs/AlGaAs 2D electron system. Sci Rep 11, 15003 (2021). https://doi.org/10.1038/s41598-021-94563-0