The effective electron mass in high-mobility SiGe/Si/SiGe quantum wells
  The effective mass, m*, of the electrons confined in high-mobility SiGe/Si/SiGe quantum wells has been measured by the analysis of the temperature dependence of the Shubnikov-de Haas oscillations. In the accessible range of electron densities, n_s, the effective mass has been found to grow with decreasing n_s, obeying the relation m*/m_b=n_s/(n_s-n_c), where m_b is the electron band mass and n_c~0.54*10^11 cm^-2. In samples with maximum mobilities ranging between 90 and 220 m^2/Vs, the dependence of the effective mass on the electron density has been found to be identical suggesting that the effective mass is disorder-independent, at least in the most perfect samples. 
M. Yu. Melnikov, A. A. Shashkin, V. T. Dolgopolov, S. V. Kravchenko,   S.-H. Huang, C. W. Liu
cond-mat.str-el cond-mat.mes-hall