Evolution of electronic structure from insulator to superconductor in Bi2Sr2-xLax(Ca,Y )Cu2 O 8+Î´
La-doped and Y-doped Bi2 Sr2 CaCu2 O 8+Î´ compounds Bi2Sr2-xLax(Ca,Y )Cu2 O8+Î´, which range from the insulator to the deeply underdoped superconductor, have been studied by angle-resolved photoemission spectroscopy. We have observed that the lower Hubbard band (LHB) of the parent insulator is gradually shifted upward with doping without significantly changing the band dispersions, which implies a downward shift of the chemical potential with hole doping. This behavior is analogous to Bi 2Sr2-xLax CuO6+Î´ and Ca 2-x Nax CuO2 Cl2 but is different from La2-x Srx CuO4, where the LHB stays well below the chemical potential and does not move while its intensity quickly diminishes in the underdoped region. Â© 2010 The American Physical Society.