Article

# 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: 38.6). 09/2004; 430(7000):650-4. DOI: 10.1038/nature02774 Source: PubMed

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**ABSTRACT:**Contrary to a widely accepted view the phase diagrams of La2−xSrxCuO4 (LSCO) and YBa2Cu3O6+y (YBCO), in spite of similarities are remarkably different. Both the electric conduction properties and the commensurate/incommensurate spin ordering properties differ dramatically. It is argued that the role of disorder in YBCO is insignificant while the bilayer structure is crucial. On the other hand in LSCO the intrinsic disorder to a large extent drives the properties of the system. The developed approach explains the low-temperature magnetic properties of the systems. The most important point is the difference with respect to the incommensurate spin ordering, including the difference in the incommensurate pitches. The understanding of mechanisms for the differences provides a deep insight into generic physics of the systems.Physical review. B, Condensed matter 05/2009; 79(17). · 3.77 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**To assess the strength of nematic fluctuations with a finite wave vector in a two-dimensional metal, we compute the static d-wave polarization function for tight-binding electrons on a square lattice. At Van Hove filling and zero temperature the function diverges logarithmically at q=0. Away from Van Hove filling the ground state polarization function exhibits finite peaks at finite wave vectors. A nematic instability driven by a sufficiently strong attraction in the d-wave charge channel thus leads naturally to a spatially modulated nematic state, with a modulation vector that increases in length with the distance from Van Hove filling. Above Van Hove filling, for a Fermi surface crossing the magnetic Brillouin zone boundary, the modulation vector connects antiferromagnetic hot spots with collinear Fermi velocities.Physical review. B, Condensed matter 02/2012; 85(16). · 3.77 Impact Factor - [Show abstract] [Hide abstract]

**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). · 0.48 Impact Factor

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