Surface acoustic wave attenuation by the localized states of a two-dimensional carrier system. in a magnetic field

The surface acoustic wave attenuation and dispersion have been measured as a function of magnetic field for both a two-dimensional electron system and a two-dimensional hole system at frequencies between 100 and 1100 MHz. The experiments were made at 350 mK in the quantum Hall regime. In the region of filling factor one where the quasi-de conductivity becomes very small, a n attenuation and dispersion is found which we attribute to localized carri er states. We estimate that the relaxation time of the localized electrons is about 60 ps while the relaxation time for localized holes is about 20 ps .