Evidence for Suppressed Screening on the Surface of High Temperature La2-xSrxCuO4 and Nd2-xCexCuO4 Superconductors

摘要: Hard x-ray photoemission spectroscopy (PES) of Cu core electronic states, with a probing depth $\ensuremath{\sim}60\text{ }\text{ }\AA{}$, is used to show that the Zhang-Rice singlet feature present in ${\mathrm{La}}_{2}{\mathrm{CuO}}_{4}$ but absent ${\mathrm{Nd}}_{2}{\mathrm{CuO}}_{4}$. Hole and electron doping ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ (LSCO) ${\mathrm{Nd}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CuO}}_{4}$ (NCCO) result new well-screened features which are missing soft PES. Impurity Anderson model calculations establish screening from doped states as its origin, strongly suppressed within 15 \AA{} surface. Complemented absorption spectroscopy, small chemical-potential shift levels ($\ensuremath{\sim}0.2\text{ }\mathrm{eV}$) shown be consistent modifications valence conduction band spanning gap ($\ensuremath{\sim}1\text{ upon hole LSCO NCCO.