Universal versus Material-Dependent Two-Gap Behaviors of the High-Tc Cuprate Superconductors: Angle-Resolved Photoemission Study of La2-xSrxCuO4

We have investigated the doping and temperature dependences of the pseudogap and superconducting gap in the single-layer cuprate La2-xSrxCuO4 by angle-resolved photoemission spectroscopy. The results clearly exhibit two distinct energy and temperature scales, namely, the gap around (pi, 0) of magnitude Delta(*) and the gap around the node characterized by the d-wave order parameter Delta(0). In comparison with Bi2212 having higher T-c's, Delta(0) is smaller, while Delta(*) and T-* are similar. This result suggests that Delta(*) and T-* are approximately material-independent properties of a single CuO2 plane, in contrast to the material-dependent Delta(0), representing the pairing strength.