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

利用交流电导率测量研究了强磁场下硅金属氧化物半导体结构二维体系的电子输运性质。在8T磁场下，在100khz ~ 10mhz的频率范围内，在0.4K ~ 1.5K的温度范围内，测量了地面朗道能级和第一激发朗道能级σ _<xx>的频率依赖性和温度依赖性。在电导率较低的地面朗道能级中，频率和温度依赖的结果表明，电子输运主要是由变程跳变控制的。第一激发朗道能级中相邻朗道能级间隙区域的结果也表明电子输运以变程跳变为主。首次证明了二维电子系统的频率依赖服从三维跳变系统的标度规律。第一激发态朗道能级峰值的结果表明，在朗道能级中心附近扩展态的输运之下，跳跃输运有相当大的贡献。

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.