Regensburg 2000 – scientific programme
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TT: Tiefe Temperaturen
TT 23: Elektronenstruktur in HTSL
TT 23.11: Talk
Friday, March 31, 2000, 12:15–12:30, H18
Suppression of superconductivity in YBa2Cu3Ox by the martensitic phase transformation at optimum doping — •J. Röhler1, G. Schröder1, and E. Kaldis2 — 1Universität zu Köln, D-50937 Köln — 2ETH Zürich, CH-8093 Zürich
YBa2Cu3Ox undergoes two martensitic phase transformations as a function of doping: i. close to the insulator-metal transition at x≃ 6.42, and ii. close to optimum doping at x=6.92. Combined analysis of atomic structure data from Y-K EXAFS and crystallographic structure data from x-ray and neutron diffraction suggests the second martensitic transformation to inhibit the further increase of Tc for dopings with x≥ 6.95. The suppression of superconductivity with the onset of the overdoped phase correlates with a sign change of the doping driven elastic strain along the c-axis, dc/dx, and in particular with a change of the dimpling in the CuO2 planes [1], thus strongly affecting the electronic interlayer hopping matrix elements. We suggest that the martensitic transformation is electronically driven and has to be considered as the structural response to the doping induced crossings of the flat parts of the Cu 3dx2−y2-O 2p band with EF at the (0,π), (π,0) points of the Brillouin zone, thus avoiding the arising singularity in the density of states at EF. The consequences for the physics of the overdoped regime in the generalized phase diagram of the cuprate superconductors are discussed.
[1] J. Röhler, S. Link, K. Conder, E. Kaldis, J. Phys. Chem. Solids 59, 1925 (1998).