Fermi surface and band dispersion in La2-xSrxCuO4

Using angle-resolved photoemission spectroscopy (ARPES), we observe the ban d structure, the Fermi surface and their doping dependences in La2-xSrxCuO4 . The results reveal that the Fermi surface undergoes a dramatic change: it is holelike and centered at (pi,pi) 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 ARP ES spectra near (pi/2,pi/2) is broad and weak unlike that in other cuprates . In the underdoped and optimally doped samples, a superconducting gap (Del ta = 10-15 meV) is observed near (pi, 0).