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TT: Tiefe Temperaturen

TT 23: Elektronenstruktur in HTSL

TT 23.11: Vortrag

Freitag, 31. März 2000, 12:15–12:30, H18

Suppression of superconductivity in YBa₂Cu₃O_x 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

YBa₂Cu₃O_x 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 T_c 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 3d_x²−y²-O 2p band with E_F at the (0,π), (π,0) points of the Brillouin zone, thus avoiding the arising singularity in the density of states at E_F. 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).