James R. Nakamura | Searcharxiv

arXiv2017

Quantum Lifetime in Ultra-High Quality GaAs Quantum Wells: Relationship to $Δ_{5/2}$ and Impact of Density Fluctuations

We consider quantum lifetime derived from low-field Shubnikov-de Haas oscillations as a metric of quality of the two-dimensional electron gas in GaAs quantum wells that expresses large excitation gaps in the fractional quantum Hall states of the N=1 Landau level. Analysis indicates two salient features: 1) small density inhomogeneities dramatically impact the amplitude of Shubnikov-de Haas oscillations such that the canonical method (cf. Coleridge, Phys. Rev. B \textbf{44}, 3793) for determination of quantum lifetime substantially underestimates $τ_q$ unless density inhomogeneity is explicitly considered; 2) $τ_q$ does not correlate well with quality as measured by $Δ_{5/2}$, the excitation gap of the fractional quantum Hall state at 5/2 filling.

cond-mat.mes-hall↗

arXiv2017

High temperature resistivity measured at ν = 5/2 as a predictor of 2DEG quality in the N=1 Landau level

We report a high temperature (T = 0.3K) indicator of the excitation gap $Δ_{5/2}$ at the filling factor $ ν=5/2$ fractional quantum Hall state in ultra-high quality AlGaAs/GaAs two-dimensional electron gases. As the lack of correlation between mobility $μ$ and $Δ_{5/2}$ has been well established in previous experiments, we define, analyze and discuss the utility of a different metric $ρ_{5/2}$, the resistivity at $ν=5/2$, as a high temperature predictor of $Δ_{5/2}$. This high-field resistivity reflects the scattering rate of composite fermions. Good correlation between $ρ_{5/2}$ and $Δ_{5/2}$ is observed in both a density tunable device and in a series of identically structured wafers with similar density but vastly different mobility. This correlation can be explained by the fact that both $ρ_{5/2}$ and $Δ_{5/2}$ are sensitive to long-range disorder from remote impurities, while $μ$ is sensitive primarily to disorder localized near the quantum well.

cond-mat.mes-hall↗