Berlin 2005 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 4: Symposium Superconducting Cuprates

TT 4.6: Vortrag

Freitag, 4. März 2005, 16:30–16:45, TU H104

Testing stripe theories: Geometry of spin excitations in the superconducting and normal state of YBa₂Cu₃O_6+x — •Vladimir Hinkov¹, Bernhard Keimer¹, Philippe Bourges², Stephane Pailhes², Yvan Sidis², Alexandre Ivanov³, Andrey Kulakov¹, Chengtian Lin¹, Dapeng Chen¹, and Christian Bernhard¹ — ¹Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany — ²Laboratoire Leon Brillouin, Saclay, France — ³Institut Laue Langevin, Grenoble, France

The physics of high-temperature cuprate superconductors exhibits a two-dimensional (2D) character due to the layered structure. An influential theory predicts a further reduction of dimensionality: In the CuO₂-layers charge and spin are supposed to separate spontaneously forming one-dimensional (1D) stripes of antiferromagnetically ordered spins separated by charge rivers. Such stripe arrangements should become visible by virtue of their quasi-1D spin excitations. We use inelastic neutron scattering (V. Hinkov et al., Nature 430, 650) to investigate the in-plane geometry of spin excitations in YBa₂Cu₃O_6+x with T_c of 90K, 61K and 35K, respectively. We use fully untwinned samples, as the signal from twinned crystals contains contributions from both perpendicular twin domains. We demonstrate, that the spin excitations are 2D and form a ring in reciprocal space, thus excluding simple, 1D arrangements of stripes. However, amplitude and width are modulated along the ring. Therefore, configurations of stripes are possible with strong orientational fluctuations, which can be quantified by our data. Further, we show that a great deal of the observed modulation originates from the normal state.