Noise spectroscopy as a tool to investigate the temperature dependence of localization in a quantum Hall system

Abstract

Generation-recombination noise in GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterostructures was investigated in the temperature range 4.2–15 K at various magnetic fields corresponding to filling factors ranging from 6 to 7. In the spectral noise intensity of the Hall voltage and in that of the longitudinal voltage, two Lorentzians arising from generation and recombination of free carriers could be distinguished. In addition thermal noise was observed. The generation-recombination noise was found to depend on temperature. Calculations based on the existence of localized states in the tails of the Landau levels were in agreement with the experimentally found Lorentzians. The temperature dependence was explained by a decrease in the number of localized states with increasing temperature. The distance between the mobility edges was found to increase proportionally with temperature. At 4.2 K this distance was estimated to be approximately equal to the width of the Landau level.