Stripe order at low temperatures in La{2-x}Sr{x}NiO4 for 1/3 < x < 1/2

Stripe order in La{2-x}Sr{x}NiO4 beyond x = 1/3 was studied with neutron scattering technique. At low temperatures, all the samples exhibit hole stripe order. Incommensurability \epsilon of the stripe order is approximately linear in the hole concentration n_h = x + 2\delta up to x = 1/2, where \delta denotes the off-stoichiometry of oxygen atoms. The charge and spin ordering temperatures exhibit maxima at n_h = 1/3, and both decrease beyond n_h > 1/3. For 1/3 < n_h < 1/2, the stripe ordering consists of the mixture of the \epsilon = 1/3 stripe order and the n_h = 1/2 charge/spin order.Comment: REVTeX, 4 pages, 4 figure

Charge Stripes and Antiferromagnetism in Insulating Nickelates and Superconducting Cuprates

Neutron and X-ray scattering studies have provided strong evidence for coupled spatial modulations of charge and spin densities in layered nickelates and cuprates. The accumulated results for La(2-x)Sr(x)NiO(4+d) are consistent with the strongly-modulated topological-stripe concept. Clues from Nd-doped La(2-x)Sr(x)CuO(4) suggest similar behavior for the cuprates. The experimental results are summarized, and features that conflict with an interpretation based on a Fermi-surface instability are emphasized. A rationalization for the differences in transport properties between the cuprates and nickelates is given.Comment: 10pp., uses elsart.sty, 3 eps figures embedded with psfig; for proceedings of Spectroscopies in Novel Superconductors '97, J. Phys. Chem. Solid

Synchrotron X-ray diffraction study of a charge stripe order in 1/8-doped La1.875_{1.875}Ba0.125−x_{0.125-x}Srx_{x}CuO4_{4}

Lattice distortions associated with charge stripe order in 1/8 hole-doped La$_{1.875}$Ba$_{0.125-x}$Sr$_{x}$CuO$_{4}$ are studied using synchrotron X-ray diffraction for $x=0.05$ and $x=0.075$. The propagation wave vector and charge order correlation lengths are determined with a high accuracy, revealing that the oblique charge stripes in orthorhombic $x=0.075$ crystal are more disordered than the aligned stripes in tetragonal $x=0.05$ crystal. The twofold periodicity of lattice modulations along the c-axis is explained by long-range Coulomb interactions between holes on neighboring CuO$_{2}$ planes.Comment: 4pages, 4figures, Submitted to PR

Modulated spin and charge densities in cuprate superconductors

Neutron scattering experiments have played a crucial role in characterizing the spin and charge correlations in copper-oxide superconductors. While the data are often interpreted with respect to specific theories of the cuprates, an attempt is made here to distinguish those facts that can be extracted empirically, and the connections that can be made with minimal assumptions.Comment: 6 pp., LaTeX, 2 col., uses espcrc2.sty + psfig.sty, 2 eps figures; Proc. of the International Conf. on Neutron Scattering, Toronto, Aug. 1997, to be published in Physica

Charge Segregation and Antiferromagnetism in High-Tc Superconductors

Local antiferromagnetism coexists with superconductivity in the cuprates. Charge segregation provides a way to reconcile these properties. Direct evidence for modulated spin and charge densities has been found in neutron and X-ray scattering studies of Nd-doped La(2-x)Sr(x)CuO(4). Here we discuss the nature of the modulation, and present some new results for a Zn-doped sample. Some of the open questions concerning the connections between segregation and superconductivity are described.Comment: 9 pp using elsart.sty, 3 eps figures included with psfig.sty, for Proc. of ISSP-7, to be published in J. Phys. Chem. Solid

Charge ordering and chemical potential shift in La2−x_{2-x}Srx_xNiO4_4 studied by photoemission spectroscopy

We have studied the chemical potential shift in La$_{2-x}$Sr$_x$NiO$_4$ and the charge ordering transition in La$_{1.67}$Sr$_{0.33}$NiO$_4$ by photoemission spectroscopy. The result shows a large ($\sim$ 1 eV/hole) downward shift of the chemical potential with hole doping in the high-doping regime ($\delta \gtrsim$ 0.33) while the shift is suppressed in the low-doping regime ($\delta \lesssim$ 0.33). This suppression is attributed to a segregation of doped holes on a microscopic scale when the hole concentration is lower than $\delta \simeq 1/3$. In the $\delta = 1/3$ sample, the photoemission intensity at the chemical potential vanishes below the charge ordering transition temperature $T_{\rm CO}=$ 240 K.Comment: 5 pages, 4 figure

Stripe orientation in an anisotropic t-J model

The tilt pattern of the CuO_6 octahedra in the LTT phase of the cuprate superconductors leads to planar anisotropies for the exchange coupling and hopping integrals. Here, we show that these anisotropies provide a possible structural mechanism for the orientation of stripes. A t_x-t_y-J_x-J_y model thus serves as an effective Hamiltonian to describe stripe formation and orientation in LTT-phase cuprates.Comment: 3 pages, 3 figure

Neutron and Synchrotron X-Ray Scattering Studies of Superconductors

Superconductors hold the promise for a more stable and efficient electrical grid, but new isotropic, high-temperature superconductors are needed in order to reduce cable manufacturing costs. The effort to understand high-temperature superconductivity, especially in the layered cuprates, provides guidance to the search for new superconductors. Neutron scattering has long provided an important probe of the collective excitations that are involved in the pairing mechanism. For the cuprates, neutron and x-ray diffraction techniques also provide information on competing types of order, such as charge and spin stripes, that appear to be closely connected to the superconductivity. Recently, inelastic x-ray scattering has become competitive for studying phonons and may soon provide valuable information on electronic excitations. Examples of how these techniques contribute to our understanding of superconductivity are presented

Charged stripes from alternating static magnetic field

We motivate and perform a calculation of the energy of a cold fluid of charged fermions in the presence of a striped magnetic background. We find that a non-trivial value for the doping density on the walls is preferredComment: RevTeX, 3 pages, 3 encapsulated PostScript figure

A Renormalization Group Analysis of Coupled Superconducting and Stripe Order in 1+1 Dimensions

In this paper we perform a renormalization group analysis on the 1+1 dimensional version of an effective field theory (previously proposed by Dung-Hai Lee, cond-mat/011393) describing (quantum) fluctuating stripe and superconductor orders. We find four possible phases corresponding to stripe order/disorder combined with superconducting order/disorder.Comment: 8 pages, 3 figures, revte