High-Frequency Hopping conductivity of Disordered 2D-system in the IQHE Regime

High frequency (hf) conductivity in the form $\sigma^{hf} = \sigma_1^{hf} - i\sigma_2^{hf}$ was obtained from the measurement of Surface Acoustic Waves (SAW) attenuation and velocity (f=30 MHz) in GaAs/AlGaAs heterostructures ($n=1.3-7\cdot 10^{11}cm^{-2}$). It has been shown that in the Integer Quantum Hall Effect (IQHE) regime for all the samples at magnetic fields corresponding to the middle of the Hall plateaus and T=1.5 K, $\sigma_1 / \sigma_2 =0.14 \pm 0.03$. The ratio $\sigma_1 / \sigma_2=0.15$ points the case when the high-frequency hopping conductivity mechanism (electronic transition between the localized states formed by "tight" pairs) is valid \cite{1}. Dependencies of $\sigma_1$ and $\sigma_2$ on temperature and magnetic field is analyzed width of the Landau band broadened by the impurity random potential is determined.