Doping dependence of two energy scales in the tunneling spectra of superconducting La2-xSrxCuO4

Scanning tunneling microscopy and spectroscopy have been performed on superconducting La2-xSrxCuO4 (x=0.06, 0.12, 0.16, and 0.2 1) at 4.2 K. Atomically resolved surface topography has been observed on the ab surface, which exhibits a one-dimensional structure corresponding to the buckling pattern of the orthorhombic phase. The tunneling spectra of all samples exhibit kinks at about +/- 5 meV in addition to the energy gap, indicating the existence of two energy scales. While the gap magnitude varies on the length scale of a few nm and steadily increases upon underdoping, the kink energy is spatially uniform on the surface and almost independent of the doping level.