Hole-concentration dependence of band structure in (Bi,Pb) ₂(Sr,La)₂CuO_6+δ determined by the angle-resolved photoemission spectroscopy

Energy-momentum (E-k) dispersion and the shape of the Fermi surface (FS) in the (Bi,Pb)₂(Sr,La)₂CuO_6+δ (Bi2201) superconductors of various hole-concentrations were investigated by the angle-resolved photoemission spectroscopy (ARPES) with high energy and momentum resolutions (ΔE = 10 meV and Δk = 0.005 Å^-1). The E-k dispersion is kept rigid and the chemical potential moves towards lower or higher energies with increasing or decreasing hole-concentration, respectively, over a wide hole-concentration range from the nearly optimal-doped condition with a transition temperature of 32K to a heavily over-doped condition where the superconducting transition disappears. By comparing the shape of the FS determined for the present Bi2201 with that reported for the Bi ₂Sr₂CaCu₂O_8+δ (Bi2212), we found that the area surrounded by the FS in the Bi2201 is fairly larger than that in the Bi2212. Estimated hole-concentration in the Bi2201 was found to vary from 0.25 to 0.43 holes/Cu, that is more than twice as large as that in the optimally doped La_2-xSr_xCuO₄ (LSCO) and Bi2212 superconductors of 0.17 holes/Cu.