Measurement of the ac quantized Hall resistance

The flatness and frequency dependence of the i=2 and four quantized Hall resistance plateaus have been investigated. It was observed that for frequencies up to 6.4 kHz, a flat region exists at the center of the plateaus where the relative resistance is constant to /spl plusmn/2/spl times/10/sup -8/, and its relative value has a linear frequency dependence of (0.119/spl plusmn/0.001) (/spl mu//spl Omega///spl Omega/)/kHz and (0.107/spl plusmn/0.007) (/spl mu//spl Omega///spl Omega/)/kHz for i=2 and 4, respectively.