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Direct angle resolved photoemission spectroscopy and superconductivity of strained high- T c films

Pavuna, Davor ; Ariosa, Daniel ; Cloetta, Dominique ; Cancellieri, Claudia ; Abrecht, Mike

In: Pramana, 2008, vol. 70, no. 2, p. 237-243

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    Titre
    • Direct angle resolved photoemission spectroscopy and superconductivity of strained high- T c films
    Auteur
    • Pavuna, Davor. Institute of Physics of Complex Matter, FSB, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland
    • Ariosa, Daniel. Institute of Physics of Complex Matter, FSB, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland
    • Cloetta, Dominique. Institute of Physics of Complex Matter, FSB, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland
    • Cancellieri, Claudia. Institute of Physics of Complex Matter, FSB, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015, Lausanne, Switzerland
    • Abrecht, Mike. Synchrotron Radiation Center, University of Wisconsin, WI-53589, Stoughton, USA
    Type de document
    • Postprint
    Identifiant OAI-PMH
    • oai:doc.rero.ch:317478
    Summary
    Since 1997 we systematically perform direct angle resolved photoemission spectroscopy (ARPES) on in-situ grown thin (<30 nm) cuprate films. Specifically, we probe low-energy electronic structure and properties of high-T c superconductors (HTSC) under different degrees of epitaxial (compressive vs. tensile) strain. In overdoped and underdoped in-plane compressed (the strain is induced by the choice of substrate) ≈15 nm thin La2 − x Sr x CuO4 (LSCO) films we almost double T c to 40 K, from 20 K and 24 K, respectively. Yet the Fermi surface (FS) remains essentially two-dimensional. In contrast, ARPES data under tensile strain exhibit the dispersion that is three-dimensional, yet T c drastically decreases. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO2 plane, enhances the two-dimensional character of the dispersion and increases T c, while the tensile strain acts in the opposite direction and the resulting dispersion is three-dimensional. We have established the shape of the FS for both cases, and all our data are consistent with other ongoing studies, like EXAFS. As the actual lattice of cuprates is like a ‘Napoleon-cake', i.e. rigid CuO2 planes alternating with softer ‘reservoir', that distort differently under strain, our data rule out all oversimplified two-dimensional (rigid lattice) mean field models. The work is still in progress on optimized La-doped Bi-2201 films with enhanced T c