Münster 1997 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 13: HTSL: Ramanstreuung, elektronische Struktur

TT 13.10: Vortrag

Mittwoch, 19. März 1997, 17:15–17:30, F2

Local Structure Studies of the Underdoped–Overdoped Transition in YBa₂Cu₃O_x by Y EXAFS — •J. Röhler¹, P.W. Loeffen², S. Link¹, K. Conder³, and E. Kaldis³ — ¹Uni Köln, D-50937 Köln — ²ESRF, F-38043 Grenoble — ³ETH, CH-8093 Zürich

We have studied the local distortions in the dimpled CuO₂ layers of YBa₂Cu₃O_x across the underdoped to the overdoped regime, x=6.801–6.984, and at T=20-300 K by yttrium K-edge extended x-ray absorption-fine-structure spectroscopy (EXAFS). In the underdoped regime doping is found to move the Cu2 atoms out of the planes by tilting the oxygen layer antiferrodistortively. At T>T_c the Cu2 displacements exhibit steps close to the so-called spin gap temperatures. In the optimum and overdoped samples no such anomalies are found in the normal state, however at T<T_c. Optimum doping appears to be a distinguished point in the phase diagram where the average atomic displacements in the CuO₂ layers turn out to be independent on temperature in the superconducting phase at T<80 K.