Improved AC quantized Hall measurements

AC quantized Hall resistance (QHR) measurements have been performed with an improved probe and sample mounting system. We describe investigations of the structure of the R/sub H/ plateau for a range of sample currents and temperatures, and for different wiring configurations. We have observed R/sub xx/ minima smaller than 0.02/spl times/10/sup -6/ of R/sub H/, an order of magnitude smaller than most published values.