Abstract
A metallic state with a vanishing activation gap, at a filling factor nu = 8/5 in the untilted specimen with n= 2 times 10^{11} cm^{-2}, and at nu = 4/3 at n=1.2 times 10^{11} cm^{-2} under a theta = 66^{0} 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 nu =8/5, and at nu =4/3 under tilt as mentioned above, over the interval 1 le nu le 2, that also includes the nu = 3/2 state, which appears perceptibly gapped in the first instance.
Highlights
A metallic state with a vanishing activation gap, at a filling factor ν = 8/5 in the untilted specimen with n
At even higher magnetic fields, Rxx minima associated with FQHE become observable, and the most prominent FQHE associated with the p/q = 5/3 and the p/q = 4/3 state have been marked here along with the filling factor ν = 3/225
We have studied the absence of FQHE at 8/5 at θ = 00 and n = 2 × 1011cm−2, and at 4/3 at θ = 660 and n = 1.2 × 1011cm−2, which is presumably induced by the coming together in energy of different polarization states associated with the 8/5 and 4/3 FQHE, respectively
Summary
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 We show that such a marginal metallic state occurs most prominently in a n = 2 × 1011cm−2 case at 8/5 for the untilted 2DES, and in a n = 1.2 × 1011cm−2 case at 4/3 under θ = 660 tilt as mentioned above, over the interval1 ≤ ν ≤ 2 , that includes the ν = 3/2 state, which appears perceptibly gapped in the first instance
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