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TT: Tiefe Temperaturen

TT 3: Elektronische Eigenschaften von HTSL

TT 3.4: Talk

Monday, March 22, 1999, 11:15–11:30, F3

Re-appearance of the Pseudogap in the Overdoped Regime of YBa₂Cu₃O_x — •J. Röhler¹, C. Friedrich¹, and E. Kaldis² — ¹Universität zu Köln, D-50937 Köln — ²ETH Zürich, CH-8093 Zürich

The electronic structure of the cuprate superconductors is known to exhibit a pseudogap in the normal phase at T^*≥ T_c. Evidence for a possible correlation between the opening of the pseudogap and anomalous displacements of Cu2 and O2,3 perpendicular to the planes of YBa₂Cu₃O_x was recently obtained from x- and T-dependent yttrium EXAFS [1]. We report on systematic EXAFS measurements covering the underdoped and overdoped regimes. The phase boundary line defined by T^*(x) is found to exhibit a V-shaped behaviour centered at T_c(x_optimum), indicating the pseudogap to re-appear in the overdoped regime. The re-appearance of the pseudogap in the overdoped regime is discussed in terms of electronic phase separation, and implications for two-subsystem models of high-temperature superconductivity are adressed.

[1] J. Röhler, S. Link, K. Conder, E. Kaldis, J. Phys. Chem. Solids (1998), in press.