Two-dimensional geometry of spin excitations in the high-transition-temperature superconductor YBa2Cu3O6+x.

Max-Planck-Institut für Festkörperforschung, 70569 Stuttgart, Germany.
Nature (Impact Factor: 42.35). 09/2004; 430(7000):650-4. DOI: 10.1038/nature02774
Source: PubMed

ABSTRACT The fundamental building block of the copper oxide superconductors is a Cu4O4 square plaquette. The plaquettes in most of these materials are slightly distorted to form a rectangular lattice, for which an influential theory predicts that high-transition-temperature (high-T(c)) superconductivity is nucleated in 'stripes' aligned along one of the axes. This theory received strong support from experiments that indicated a one-dimensional character for the magnetic excitations in the high-T(c) material YBa2Cu3O6.6 (ref. 4). Here we report neutron scattering data on 'untwinned' YBa2Cu3O6+x crystals, in which the orientation of the rectangular lattice is maintained throughout the entire volume. Contrary to the earlier claim, we demonstrate that the geometry of the magnetic fluctuations is two-dimensional. Rigid stripe arrays therefore appear to be ruled out over a wide range of doping levels in YBa2Cu3O6+x, but the data may be consistent with liquid-crystalline stripe order. The debate about stripes has therefore been reopened.

  • 01/2013;
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    ABSTRACT: High-temperature superconductors exhibit a characteristic hourglass-shaped spectrum of magnetic fluctuations which most likely contribute to the pairing glue in the cuprates. Recent neutron scattering experiments in strongly underdoped compounds have revealed a significant low energy anisotropy of these fluctuations which we explain by a model in which topological defects of the antiferromagnet clump to producing domain wall segments with ferronematic order. This state does not invoke global charge order but breaks C4 rotational and inversion symmetry. The incommensurability of the low doping charge-disordered state is in good agreement with experiment and interpolates smoothly with the incommensurability of the stripe phase at higher doping. Within linear spin-wave theory the dynamic structure factor is in very good agreement with inelastic neutron scattering data and can account for the observed energy dependent anisotropy.
    Scientific Reports 06/2014; 4:5319. · 5.08 Impact Factor
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    ABSTRACT: We study the effects of spin-antisymmetric interactions on the stability of a Landau–Fermi liquid on the square lattice, using the generalized Pomeranchuk method for two-dimensional lattice systems. In particular, we analyze interactions that could induce instabilities of the so-called spin-split type, that is when spin-up and spin-down Fermi surfaces are displaced with respect to each other. The phase space is studied as a function of the strength of the interaction V, the electron chemical potential μ and an external magnetic field h. We find that such interactions produce in general an enhancement of the instability region of the Landau–Fermi liquid. More interestingly, in certain regions of the V–μ phase space, we find a reentrant behavior as a function of the magnetic field h, similar to that found in recent experiments, e.g. in URu2Si2 and Sr3Ru2O7.
    Modern Physics Letters B 06/2012; 26(19). · 0.69 Impact Factor

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