Berlin 2008 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 15: Superconductivity: Poster Session

TT 15.9: Poster

Tuesday, February 26, 2008, 14:00–18:00, Poster B

In-plane anisotropy of the spin excitation spectrum in strongly underdoped YBa₂Cu₃O_6+x — •Daniel Haug¹, Vladimir Hinkov¹, Benoît Fauqué², Philippe Bourges², Yvan Sidis², Alexandre Ivanov³, Chengtian Lin¹, and Bernhard Keimer¹ — ¹Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany — ²Laboratoire Léon Brillouin, CEA-CNRS Saclay, France — ³Institut Laue-Langevin, Grenoble, France

The spin excitation spectrum of the optimally doped and moderately underdoped high-temperature superconductor YBa₂Cu₃O_6+x is dominated by the so-called resonance peak for excitation energies between 30 and 40 meV (depending on the oxygen content x) that sets in abruptly below T_c. Here we report measurements on arrays of untwinned single crystals in the strongly underdoped regime in which the situation is very different: Spectral weight is shifted towards low energies and evolves smoothly through T_c. The spectrum exhibits a peak below ∼10 meV which shows a spontaneous onset of a strong anisotropy in the a-b-plane defined by the CuO₂ layers. This phenomenon matches the symmetry properties of a nematic liquid crystal, a new symmetry-broken electronic phase that coexists with high-temperature superconductivity in strongly underdoped cuprates.