Frequency scaling of microwave conductivity in the integer quantum Hall effect minima

We measure the longitudinal conductivity σ_xx at frequencies 1.246 GHz<=f<=10.05 GHz over a range of temperatures 235 mK<=T<=4.2 K with particular emphasis on the quantum Hall plateaus. We find that Re(σ_xx) scales linearly with frequency for a range of magnetic field around the center of the plateaus, i.e., where σ_xx(ω)>>σ^dc_xx. The width of this scaling region decreases with higher temperature and vanishes by 1.2 K altogether. Comparison between localization length determined from σ_xx(ω) and dc measurements on the same wafer show good agreement.