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

Abstract

A metallic state with a vanishing activation gap, at a filling factor ν= 8 / 5 in the untilted specimen with n= 2 × 10 11cm- 2, and at ν= 4 / 3 at n= 1.2 × 10 11cm- 2 under a θ= 66 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 the ν= 3 / 2 state, which appears perceptibly gapped in the first instance.