Doping Evolution of the Underlying Fermi Surface in La2-xSrxCuO4
  We have performed a systematic doping dependent study of La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) (0.03$\leq x \leq$0.3) by angle-resolved photoemission spectroscopy. In the entire doping range, the underlying ``Fermi surface" determined from the low energy spectral weight approximately satisfies Luttinger's theorem, even down to the lightly-doped region. This is in strong contrast to the result on Ca$_{2-x}$Na$_x$CuO$_2$Cl$_2$ (Na-CCOC), which shows a strong deviation from Luttinger's theorem. The differences between LSCO and Na-CCOC are correlated with the different behaviors of the chemical potential shift and spectral weight transfer induced by hole doping. 
T. Yoshida, X. J. Zhou, K. Tanaka, W. L. Yang, Z. Hussain, Z.-X. Shen,   A. Fujimori, Seiki Komiya, Yoichi Ando, H. Eisaki, ...