X-ray Absorption Studies of YBa2Cu3O(6+x), La(2-x)Sr(x)CuO4, and Nd(2-x)Ce(x)CuO4.

摘要

O K-edge absorption studies show that the density of O 2p empty states near the Fermi level increases with increasing oxygen content for YBa(sub 2)Cu(sub 3)O(sub 6+x), and Sr concentration in La(sub 2-x)Sr(sub x)CuO(sub 4). With Zn substitution for Cu in YBa(sub 2)Cu(sub 3)O(sub 7), (Tc) does not correlate with the density of O 2p empty states. In this case Tc dramatically decreases with Zn substitution while the pre-edge feature remains unchanged. The O K-edge spectrum of Nd(sub 2-x)Ce(sub x)CuO(sub 4) barely changes from the undoped, insulating, to the Ce doped superconducting sample. The lack of unoccupied O 2p states near the Fermi level in this case is consistent with naive expectations for electron-doping. 21 refs., 4 figs.