X-Ray Absorption Near-Edge Studies of La_2-xSr_xCuO_4-y

Abstract

The effect of hole doping on the electron states at the copper sites in La 2- x Sr x CuO 4- y (0.0< x <0.25) has been studied by the X-ray absorption near-edge structure on the Cu K-edge. We find that the absorption edge shifts to a higher energy with the increase of Sr concentration x and saturates at x =0.20, coinciding with x having the maximum value of T c . The observed systematic edge shift indicates that doping infiuences the electron states on the copper sites either directly, by the formation of the Cu d hole (d 8 configuration) or indirectly, through the distortion of the CuO 6 unit.