Microwave frequency dependence of integer quantum Hall effect: Evidence for finite-frequency scaling

We present ac measurements of the diagonal conductivity σₓₓ, in the integer quantum Hall regime for frequency f between 0.2 and 14 GHz and temperature T{≥}50 mK. Re(σₓₓ) was obtained from the measured attenuation of a coplanar transmission line on the sample surface. For f{}1 GHz, σₓₓ peaks between IQHE minima broaden as f increases, roughly as ({Δ}B){∝}f^γ, where {Δ}B is the peak width. {γ}=0.41±{}0.04 for spin-split peaks, and for spin-degenerate peaks {γ}=0.20±{}0.05. We interpret our data in terms of dynamic scaling. Our {γ}, when compared with existing estimates of the localization length exponent {ν}, is consistent with assigning a dynamic exponent z=1.