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

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

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 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 stripes in cuprate superconductors: The middle way

Charge and spin stripe order is a type of electronic crystal observed in certain layered cuprates associated with high-temperature superconductivity. Quantum-disordered stripes could be relevant for understanding the superconductivity. Here I discuss recent experimental characterizations of the stripe-ordered state in La(1.875)Ba(0.125)CuO(4), and compare them with properties of superconducting compositions.Comment: 6 pp., submitted to the proceedings of ECRYS 2005, J. Phys. I

Dynamical stripe correlations and the spin fluctuations in cuprate superconductors

It is conjectured that the anomalous spin dynamics observed in the normal state of cuprate superconductors might find its origin in a nearly ordered spin system which is kept in motion by thermally meandering charged domain walls. `Temperature sets the scale' finds a natural explanation, while a crossover to a low temperature quantum domain wall fluid is implied.Comment: 3 pages Revtex. To appear in Physica

Experimental Evidence for Topological Doping in the Cuprates

Some recent experiments that provide support for the concept of topological doping in cuprate superconductors are discussed. Consistent with the idea of charge segregation, it is argued that the scattering associated with the ``resonance'' peak found in YBa(2)Cu(3)O(6+x) and Bi(2)Sr(2)CaCu(2)O(8+\delta) comes from the Cu spins and not from the doped holes.Comment: 5 pp., uses aipproc.sty, for Proc. of U. Miami Conf: HTS9

Stripes and superconductivity in cuprate superconductors

One type of order that has been observed to compete with superconductivity in cuprates involves alternating charge and antiferromagnetic stripes. Recent neutron scattering studies indicate that the magnetic excitation spectrum of a stripe-ordered sample is very similar to that observed in superconducting samples. In fact, it now appears that there may be a universal magnetic spectrum for the cuprates. One likely implication of this universal spectrum is that stripes of a dynamic form are present in the superconducting samples. On cooling through the superconducting transition temperature, a gap opens in the magnetic spectrum, and the weight lost at low energy piles up above the gap; the transition temperature is correlated with the size of the spin gap. Depending on the magnitude of the spin gap with respect to the magnetic spectrum, the enhanced magnetic scattering at low temperature can be either commensurate or incommensurate. Connections between stripe correlations and superconductivity are discussed.Comment: 6 pp, for proceedings of SPIE mtg., July 31-Aug. 4, 2005 in San Dieg

Charge stripes and spin correlations in copper-oxide superconductors

Recent neutron diffraction studies have yielded evidence that, in a particular cuprate family, holes doped into the CuO(2) planes segregate into stripes that separate antiferromagnetic domains. Here it is shown that such a picture provides a quantitatively consistent interpretation of the spin fluctuations measured by neutron scattering in La(1.85)Sr(0.15)CuO(4) and YBa(2)Cu(3)O(6+x).Comment: 4 pp., LaTeX, uses espcrc2.sty, 2 eps figures included with psfig, for proceedings of M2S-HTSC-