Berlin 2008 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 29: Superconductivity: Mechanisms, Phase Diagram, Competing Order

TT 29.8: Hauptvortrag

Donnerstag, 28. Februar 2008, 11:30–12:00, H 3010

Charge redistribution at YBCO-metal interfaces — •Udo Schwingenschlögl and Cosima Schuster — Institut für Physik, Universität Augsburg, D-86135 Augsburg

Charge redistribution at YBCO-metal interfaces is crucial for technological applications of YBCO superconductors, since the band structure is modified on a local scale. In particular, the superconducting CuO₂ planes are intrinsically electron doped (underdoped) due to the metallic contact. In order to obtain quantitative insight into this intrinsic doping mechanism, the normal-state YBCO electronic structure close to YBCO-metal interfaces is studied by means of first-principles band calculations, based on density functional theory. Because of a strong lattice relaxation, it is essential to carry out a detailed structure optimization, which is done for prototypical interface geometries. Additional defects or substitution of the cations may support or compensate the charge transfer. Oxygen vacancies, for instance, tend to locally underdope the superconductor. Intentional overdoping by substituting Y by Ca, on the other hand, compensates this effect and therefore can be used to enhance the critical current density. In addition, effects of electronegative impurities, like F or Cl, are of interest, particularly as concerns the re-extraction of charge from an underdoped YBCO-metal interface.