We have studied the chemical potential shift in the high-temperature superconductor Bi$_2$Sr$_2$Ca$_{ 1-x}${ \it R}$_{ x}$Cu$_2$O$_{ 8+y}$ ({ \it R} = Pr, Er), where the hole concentration is varied from 0.025 to 0.17 per Cu, by precise measurements of core-level photoemission spectra. The result shows that the shift becomes slow in the underdoped region as in the case of La$_{ 2-x}$Sr$_{ x}$CuO$_{ 4}$ (LSCO) but the effect is much weaker than in LSCO. The observed shift in the present system can be relatively well explained by numerical results on the doped two-dimensional Hubbard model, and suggests that the change of the electronic structure induced by hole doping is less influenced by stripe fluctuations than in LSCO.
Categories: cond-mat.supr-con cond-mat.str-el