title: Direct evidence for negative grain boundary potential in Ca-doped and undoped YBa2Cu3O7-x.
abstract: Using electron holography in a transmission electron microscope, we obtained direct evidence for the reduction of negative charge at grain boundary dislocations in Ca-doped YBa2Cu3O7 (YBCO) when compared to undoped YBCO. Because of the finite width of the valence band in the superconducting CuO2 planes, the negative grain boundary charge can lead to a depletion of electron holes available for superconductivity. A significant reduction in the size of the perturbed region in the Ca-doped samples appears to be the principal mechanism for the improved interfacial superconductivity.
authors.affiliation: Brookhaven National Laboratory, Upton, New York 11973, USA. schofield@bnl.gov
authors.forename: Marvin A
authors.initials: MA
authors.lastname: Schofield
authors.forename: Marco
authors.initials: M
authors.lastname: Beleggia
authors.forename: Yimei
authors.initials: Y
authors.lastname: Zhu
authors.forename: Karsten
authors.initials: K
authors.lastname: Guth
authors.forename: Christian
authors.initials: C
authors.lastname: Jooss