Dresden 2003 – scientific programme

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TT: Tiefe Temperaturen

TT 3: Supraleitung: Elektronenstruktur, Phononen, Tunneln, Ordnungsparameter I

TT 3.8: Talk

Monday, March 24, 2003, 11:15–11:30, HSZ301

Doping dependence of the disorder in the CuO₂ planes of Bi₂Sr_2−xLa_xCuO_6+δ — •J. Röhler¹, M. Klinkmann¹, H. Hess¹, R. Manzke², H. Dwelk², and A. Krapf² — ¹Universität zu Köln, D-50937 Köln — ²Humboldt-Universität zu Berlin, D-10115 Berlin

An inhomogeneous electronic structure and disorder in the CuO₂ planes are frequently considered to be essential features of the superconductivity in the cuprates. Experimental evidence for an “optimum inhomogeneity” or the survival of one-dimensional patterns at the underdoped-overdoped transition around T_cmax is however still controversial, in particular in the most intensively studied single layer system La_2−xSr_xCuO₄. We report the doping dependence of the structural disorder in the CuO₂ planes of the single layer system Bi₂Sr_2−xLa_xCuO_6+δ as obtained from measurements of the extended absorption fine structure (EXAFS) beyond the Cu-K absorption edge. While substitution of Sr by La drives the system from the overdoped through the underdoped regimes to the insulating phase, the crystallographic structure keeps its nominal orthorhombic symmetry. From the analysis of the multiple scattering channels (Cu, O1, Cu) of the photoelectrons in the CuO₂ plane we find a strong doping dependence of the O1 c-axis displacements, exhibiting a sharp minimum around optimum doping. We conclude that structural disorder and possibly related electronic inhomogeneities are minimized at T_cmax. They increase strongly towards both, the strongly overdoped metallic, and the insulating phases. The results on the structural disorder are discussed together with recent O-K absorption and photoemission data.