Chemical potential shift inNd2−xCexCuO4: Contrasting behavior between the electron- and hole-doped cuprates

We have studied the chemical potential shift in the electron-doped superconductor ${\mathrm{Nd}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_4$ by precise measurements of core-level photoemission spectra. The result shows that the chemical potential monotonously increases with electron doping, quite differently from ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4,$ where the shift is suppressed in the underdoped region. If the suppression of the shift in ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x{\mathrm{CuO}}_4$ is attributed to strong stripe fluctuations, the monotonous increase of the chemical potential is consistent with the absence of stripe fluctuations in ${\mathrm{Nd}}_{2-x}{\mathrm{Ce}}_x{\mathrm{CuO}}_4.$ The chemical potential jump between ${\mathrm{Nd}}_2{\mathrm{CuO}}_4$ and ${\mathrm{La}}_2{\mathrm{CuO}}_4$ is suggested to be much smaller than the optical band gaps.