Coexistence of a pseudogap and a superconducting gap for the high-Tc superconductor La2-xSrxCuO4 studied by angle-resolved photoemission spectroscopy

The relationship between the superconducting gap and the pseudogap has been the subject of controversies. In order to clarify this issue, we have studied the superconducting gap and pseudogap of the high-Tc superconductor La2-xSrxCuO4 (x=0.10,14) by angle-resolved photoemission spectroscopy (ARPES). Through the analysis of the ARPES spectra above and below Tc, we have identified a superconducting coherence peak even in the antinodal region on top of the pseudogap of a larger energy scale. The superconducting peak energy nearly follows the pure d-wave form. The d-wave order parameter Δ0 [defined by Δ(k)=Δ0(coskxa-coskya)] for x=0.10 and 0.14 are nearly the same, Δ0∼12-14meV, leading to strong coupling 2Δ0/kBTc∼10. The present result indicates that the pseudogap and the superconducting gap are distinct phenomena and can be described by the "two-gap" scenario.