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

Abstract

We report measurements of microwave spectra of two-dimensional electron systems hosted in dilute Al alloy, Al x Ga 1−x As, 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 alloydisordered 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.

Magnetophonons & type-B Goldstones from hydrodynamics to holography

“…As we will see, holography is indeed one of the cases where this does not happen. More interestingly and broadly, the dynamics of the magnetophonon peak as a function of the magnetic field can reveal the fundamental nature of the "disorder" responsible for its pinning [39][40][41][42][43][44][45], and it thus encodes a very valuable insight into the system at hand. In the following section 2, we will provide more details about the physics of magnetophonon resonances.…”

Magnetotransport patterns of collective localization near $ν=1$ in a high-mobility two-dimensional electron gas

“…While it is generally thought that disorder suppresses a collective phase such as the IQHWS, under special circumstances disorder may stabilize a Wigner solid in a region where the Wigner solid did not form in the absence of disorder. Such a scenario was realized in samples in which a short range disorder was embedded into the channel during the molecular beam epitaxy growth [35,36] and in which a Wigner solid developed near ν ≈ 0.6. Complex disorder effects are also likely at play in the formation of other collective insulators, such as the BPs in high Landau levels [20,21].…”

Exploring Quantum Hall Physics at Ultra-Low Temperatures and at High Pressures

“…Experiments on such alloy samples had a strong impact on the understanding of the plateau-to-plateau transition in the integer quantum Hall regime, 49,175 mapping the electronic wavefunction along a direction perpendicular to the plane of the 2DEG, 186 and contributed to understanding of pinning of Wigner crystals. 187 Another successful experiment was performed on alloy samples that enabled the study of the FQHS at ν = 5/2 in the presence of alloy disorder. 185,188 These samples were based on modern sample structures assuring the high density, near n 3 × 10 11 cm −2 , and high quality necessary for robust second Landau level fractional quantum Hall states.…”