Microwave pinning modes near Landau filling ν=1 in two-dimensional electron systems with alloy disorder

الأصل · EN

We report measurements of microwave spectra of two-dimensional electron systems hosted in dilute Al alloy, AlₓGa₁₋ₓAs, for a range of Landau level fillings, ν, around 1. For ν>0.8 or ν<1.2, the samples exhibit a microwave resonance whose frequency decreases as ν moves away from 1. A resonance with this behavior is the signature of solids of quasiparticles or -holes in the partially occupied Landau level, which was previously seen in ultralow disorder samples. For ν<0.8 down to as low as ν=0.54, a resonance in the spectra is still present in the Al alloy-disordered samples, though it is partially or completely suppressed at ν=3/5 and 1/2, and is strongly damped over much of this ν range. The resonance also shows a striking enhancement in peak frequency for ν just below 3/4. We discuss possible explanations of the resonance behavior for ν<0.8 in terms of the composite fermion picture.