Evolution of electronic structure from insulator to superconductor inBi2Sr2−xLax(Ca,Y)Cu2O8+δ

Abstract

La-doped and Y-doped ${\text{Bi}}_{2}{\text{Sr}}_{2}{\text{CaCu}}_{2}{\text{O}}_{8+\ensuremath{\delta}}$ compounds ${\text{Bi}}_{2}{\text{Sr}}_{2\ensuremath{-}x}{\text{La}}_{x}(\text{Ca},\text{Y}){\text{Cu}}_{2}{\text{O}}_{8+\ensuremath{\delta}}$, 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 ${\text{Bi}}_{2}{\text{Sr}}_{2\ensuremath{-}x}{\text{La}}_{x}{\text{CuO}}_{6+\ensuremath{\delta}}$ and ${\text{Ca}}_{2\ensuremath{-}x}{\text{Na}}_{x}{\text{CuO}}_{2}{\text{Cl}}_{2}$ but is different from ${\text{La}}_{2\ensuremath{-}x}{\text{Sr}}_{x}{\text{CuO}}_{4}$, where the LHB stays well below the chemical potential and does not move while its intensity quickly diminishes in the underdoped region.