HIGH FREQUENCY CONDUCTIVITY OF GROUND LANDAU LEVELS IN SILICON MOS TWO DIMENSIONAL ELECTRON SYSTEMS

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The electronic transport properties of two-dimensional systems of a silicon MOS (Metal-Oxide-Semiconductor) structure under strong magnetic fields wewe investigated using AC conductivity measurements. Frequnecy dependence and temperature dependence of sigma _<xx> in the ground Landau levels and the first excited Landau levels has been measured at frequncy between 100 kHz and 10 MHz and at a temperature between 0.4K and 1.5K in a magnetic field of 8T.Both results of frequncy and temperature dependence in the ground Landau levels, where the conductivity exhibits low values, have shown that the electronic transport was dominated by the variable range hopping. Results in the gap regions between the adjacent Landau levels in the first excited Landau levels have also shown that the electronic tarnsport was dominated by variable range hopping. It was first demonstrated that the frequency dependence in the two dimensional electron systems obey the scaling law observed in three dimensional hopping systems.Results in the peak of the first excited Landau levels have shown that there have been a considerable contribution of the hopping transport underling the transport in the extended states near the center of the Landau level.