Quantum lifetime in ultrahigh quality GaAs quantum wells: Relationship to Δ5/2 and impact of density fluctuations
AbstractWe consider the quantum lifetime derived from low-field Shubnikov–de Haas oscillations as a metric of the quality of the two-dimensional electron gas in GaAs quantum wells that expresses large excitation gaps of the ν=52 fractional quantum Hall state in the N=1 Landau level. In high quality samples, small density inhomogeneities dramatically impact the amplitude of Shubnikov–de Haas oscillations such that the canonical method [cf. Coleridge, Phys. Rev. B 44, 3793 (1991)10.1103/PhysRevB.44.3793] for determination of the quantum lifetime substantially underestimates τq unless density inhomogeneity is explicitly considered. We have developed a method that can be used to determine density inhomogeneity and extract the intrinsic τq by analyzing the Shubnikov–de Haas oscillations. However, even after accounting for inhomogeneity, τq does not correlate well with sample quality as measured by Δ5/2, the excitation gap of the fractional quantum Hall state at 5/2 filling.