Fermi surface and band dispersion in La_2-xSr_xCuO₄

Using angle-resolved photoemission spectroscopy (ARPES), we observe the band structure, the Fermi surface and their doping dependences in La_2-xSr_xCuO₄. The results reveal that the Fermi surface undergoes a dramatic change: it is holelike and centered at (π.π) in underdoped (x = 0.1) and optimally doped (x = 0.15) samples as in other cuprates. while it is electronlike and centered at (0, 0) in heavily overdoped (x = 0.3) ones. The peak in the ARPES spectra near (π/2, π/2) is broad and weak unlike that in other cuprates. In the underdoped and optimally doped samples, a superconducting gap (Δ = 10-15 meV) is observed near (π, 0).