Experimental Studies of Low-field Landau Quantization in Two-dimensional   Electron Systems in GaAs/AlGaAs Heterostructures
  By applying a magnetic field perpendicular to GaAs/AlGaAs two-dimensional electron systems, we study the low-field Landau quantization when the thermal damping is reduced with decreasing the temperature. Magneto-oscillations following Shubnikov-de Haas (SdH) formula are observed even when their amplitudes are so large that the deviation to such a formula is expected. Our experimental results show the importance of the positive magneto-resistance to the extension of SdH formula under the damping induced by the disorder. 
Jing-Han Chen, D. R. Hang, C. F. Huang, Tsai-Yu Huang, Jyun-Ying Lin,   S. H. Lo, J. C. Hsiao, Ming-Gu Lin, M.Y. Simmons, D....