24,046 research outputs found

    Rotated stripe order and its competition with superconductivity in La1.88_{1.88}Sr0.12_{0.12}CuO4_4

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    We report the observation of a bulk charge modulation in La1.88_{1.88}Sr0.12_{0.12}CuO4_4 (LSCO) with a characteristic in-plane wave-vector of (0.236, ±Ύ\pm \delta), with Ύ\delta=0.011 r.l.u. The transverse shift of the ordering wave-vector indicates the presence of rotated charge-stripe ordering, demonstrating that the charge ordering is not pinned to the Cu-O bond direction. On cooling through the superconducting transition, we find an abrupt change in the growth of the charge correlations and a suppression of the charge order parameter indicating competition between the two orderings. Orthorhombic LSCO thus helps bridge the apparent disparities between the behavior previously observed in the tetragonal "214" cuprates and the orthorhombic yttrium and bismuth-based cuprates and thus lends strong support to the idea that there is a common motif to charge order in all cuprate families.Comment: 6 pages, 4 figue

    Entanglement and spin squeezing in the two-atom Dicke model

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    We analyze the relation between the entanglement and spin-squeezing parameter in the two-atom Dicke model and identify the source of the discrepancy recently reported by Banerjee and Zhou et al that one can observe entanglement without spin squeezing. Our calculations demonstrate that there are two criteria for entanglement, one associated with the two-photon coherences that create two-photon entangled states, and the other associated with populations of the collective states. We find that the spin-squeezing parameter correctly predicts entanglement in the two-atom Dicke system only if it is associated with two-photon entangled states, but fails to predict entanglement when it is associated with the entangled symmetric state. This explicitly identifies the source of the discrepancy and explains why the system can be entangled without spin-squeezing. We illustrate these findings in three examples of the interaction of the system with thermal, classical squeezed vacuum and quantum squeezed vacuum fields.Comment: 7 pages, 1 figur

    Coloron Phenomenology

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    A flavor-universal extension of the strong interactions was recently proposed in response to the apparent excess of high-ETE_T jets in the inclusive jet spectrum measured at the Tevatron. This paper studies the color octet of massive gauge bosons (`colorons') that is present in the low-energy spectrum of the model's Higgs phase. Constraints from searches for new particles decaying to dijets and from measurements of the weak-interaction ρ\rho parameter imply that the colorons must have masses greater than 870-1000 GeV. The implications of recent Tevatron data and the prospective input from future experiments are also discussed.Comment: 13 pages, 4 embedded Postscript figures, LaTeX, full postscript version also available at http://smyrd.bu.edu/htfigs/htfigs.html rectified confusing phrase at end of sub-section on 'dijets

    Influence of the single-particle Zeeman energy on the quantum Hall ferromagnet at high filling factors

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    In a recent paper [B. A. Piot et al., Phys. Rev. B 72, 245325 (2005)], we have shown that the lifting of the electron spin degeneracy in the integer quantum Hall effect at high filling factors should be interpreted as a magnetic-field-induced Stoner transition. In this work, we extend the analysis to investigate the influence of the single-particle Zeeman energy on the quantum Hall ferromagnet at high filling factors. The single-particle Zeeman energy is tuned through the application of an additional in-plane magnetic field. Both the evolution of the spin polarization of the system and the critical magnetic field for spin splitting are well described as a function of the tilt angle of the sample in the magnetic field.Comment: Published in Phys. Rev.

    Universal Static and Dynamic Properties of the Structural Transition in Pb(Zn1/3Nb2/3)O3

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    The relaxors Pb(Zn1/3_{1/3}Nb2/3_{2/3})O3_{3} (PZN) and Pb(Mg1/3_{1/3}Nb2/3_{2/3})O3_{3} (PMN) have very similar properties based on the dielectric response around the critical temperature TcT_{c} (defined by the structural transition under the application of an electric field). It has been widely believed that these materials are quite different below TcT_{c} with the unit cell of PMN remaining cubic while in PZN the low temperature unit cell is rhombohedral in shape. However, this has been clarified by recent high-energy x-ray studies which have shown that PZN is rhombohedral only in the skin while the shape of the unit cell in the bulk is nearly cubic. In this study we have performed both neutron elastic and inelastic scattering to show that the temperature dependence of both the diffuse and phonon scattering in PZN and PMN is very similar. Both compounds show a nearly identical recovery of the soft optic mode and a broadening of the acoustic mode below TcT_{c}. The diffuse scattering in PZN is suggestive of an onset at the high temperature Burns temperature similar to that in PMN. In contrast to PMN, we observe a broadening of the Bragg peaks in both the longitudinal and transverse directions below TcT_{c}. We reconcile this additional broadening, not observed in PMN, in terms of structural inhomogeneity in PZN. Based on the strong similarities between PMN and PZN, we suggest that both materials belong to the same universality class and discuss the relaxor transition in terms of the three-dimensional Heisenberg model with cubic anisotropy in a random field.Comment: 11 pages, 10 figures. Updated version after helpful referee comment

    Momentum-Resolved Charge Excitations in a Prototype One Dimensional Mott Insulator

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    We report momentum resolved charge excitations in a one dimensional (1-D) Mott insulator studied using high resolution (~ 325 meV) inelastic x-ray scattering over the entire Brillouin zone for the first time. Excitations at the insulating gap edge are found to be highly dispersive (momentum dependent)compared to excitations observed in two dimensional Mott insulators. The observed dispersion in 1-D is consistent with charge excitations involving holons which is unique to spin-1/2 quantum chain systems. These results point to the potential utility of inelastic x-ray scattering in providing valuable information about electronic structure of strongly correlated insulators.Comment: 3 pages, 2 figures, Revised with minor change

    The transverse magnetoresistance of the two-dimensional chiral metal

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    We consider the two-dimensional chiral metal, which exists at the surface of a layered, three-dimensional sample exhibiting the integer quantum Hall effect. We calculate its magnetoresistance in response to a component of magnetic field perpendicular to the sample surface, in the low temperature, but macroscopic, regime where inelastic scattering may be neglected. The magnetoresistance is positive, following a Drude form with a field scale, B0=Ί0/alelB_0=\Phi_0/al_{\text{el}}, given by the transverse field strength at which one quantum of flux, Ί0\Phi_0, passes through a rectangle with sides set by the layer-spacing, aa, and the elastic mean free path, lell_{\text{el}}. Experimental measurement of this magnetoresistance may therefore provide a direct determination of the elastic mean free path in the chiral metal.Comment: submitted to Phys Rev
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