Systematic Cu-63 NQR studies of the stripe phase in La(1.6-x)Nd(0.4)Sr(x)CuO(4) for 0.07 <= x <= 0.25

We demonstrate that the integrated intensity of Cu-63 nuclear quadrupole resonance (NQR) in La(1.6-x)Nd(0.4)Sr(x)CuO(4) decreases dramatically below the charge-stripe ordering temperature T(charge). Comparison with neutron and X-ray scattering indicates that the wipeout fraction F(T) (i.e. the missing fraction of the integrated intensity of the NQR signal) represents the charge-stripe order parameter. The systematic study reveals bulk charge-stripe order throughout the superconducting region 0.07 <= x <= 0.25. As a function of the reduced temperature t = T/T(charge), the temperature dependence of F(t) is sharpest for the hole concentration x=1/8, indicating that x=1/8 is the optimum concentration for stripe formation.Comment: 10 pages of text and captions, 11 figures in postscript. Final version, with new data in Fig.

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

4f-spin dynamics in La(2-x-y)Sr(x)Nd(y)CuO(4)

We have performed inelastic magnetic neutron scattering experiments on La(2-x-y)Sr(x)Nd(y)CuO(4) in order to study the Nd 4f-spin dynamics at low energies. In all samples we find at high temperatures a quasielastic line (Lorentzian) with a line width which decreases on lowering the temperature. The temperature dependence of the quasielastic line width Gamma/2(T) can be explained with an Orbach-process, i.e. a relaxation via the coupling between crystal field excitations and phonons. At low temperatures the Nd-4f magnetic response S(Q,omega) correlates with the electronic properties of the CuO(2)-layers. In the insulator La(2-y)Nd(y)CuO(4) the quasielastic line vanishes below 80 K and an inelastic excitation occurs. This directly indicates the splitting of the Nd3+ ground state Kramers doublet due to the static antiferromagnetic order of the Cu moments. In La(1.7-x)Sr(x)Nd(0.3)CuO(4) with x = 0.12, 0.15 and La(1.4-x)Sr(x)Nd(0.6)CuO(4) with x = 0.1, 0.12, 0.15, 0.18 superconductivity is strongly suppressed. In these compounds we observe a temperature independent broad quasielastic line of Gaussian shape below T about 30 K. This suggests a distribution of various internal fields on different Nd sites and is interpreted in the frame of the stripe model. In La(1.8-y)Sr(0.2)Nd(y)CuO(4) (y = 0.3, 0.6) such a quasielastic broadening is not observed even at lowest temperature.Comment: 8 pages, 10 figures included, to appear in Phys. Rev.

Topological doping and the stability of stripe phases

We analyze the properties of a general Ginzburg-Landau free energy with competing order parameters, long-range interactions, and global constraints (e.g., a fixed value of a total ``charge'') to address the physics of stripe phases in underdoped high-Tc and related materials. For a local free energy limited to quadratic terms of the gradient expansion, only uniform or phase-separated configurations are thermodynamically stable. ``Stripe'' or other non-uniform phases can be stabilized by long-range forces, but can only have non-topological (in-phase) domain walls where the components of the antiferromagnetic order parameter never change sign, and the periods of charge and spin density waves coincide. The antiphase domain walls observed experimentally require physics on an intermediate lengthscale, and they are absent from a model that involves only long-distance physics. Dense stripe phases can be stable even in the absence of long-range forces, but domain walls always attract at large distances, i.e., there is a ubiquitous tendency to phase separation at small doping. The implications for the phase diagram of underdoped cuprates are discussed.Comment: 18 two-column pages, 2 figures, revtex+eps

The nature of circulating CD27+CD43+ B cells

Letter to the Editor.-- et al.M.C. van Zelm is supported by fellowships from the Erasmus University Rotterdam (EUR-Fellowship) and the Erasmus MC, and by Veni grant 916.110.90 from ZonMW/NWO.Peer Reviewe

Muon spin relaxation studies of incommensurate magnetism and superconductivity in stage-4 La2_{2}CuO4.11_{4.11} and La1.88_{1.88}Sr0.12_{0.12}CuO4_{4}

This paper reports muon spin relaxation (MuSR) measurements of two single crystals of the title high-Tc cuprate systems where static incommensurate magnetism and superconductivity coexist. By zero-field MuSR measurements and subsequent analyses with simulations, we show that (1) the maximum ordered Cu moment size (0.36 Bohr magneton) and local spin structure are identical to those in prototypical stripe spin systems with the 1/8 hole concentration; (2) the static magnetism is confined to less than a half of the volume of the sample, and (3) regions with static magnetism form nano-scale islands with the size comparable to the in-plane superconducting coherence length. By transverse-field MuSR measurements, we show that Tc of these systems is related to the superfluid density, in the same way as observed in cuprate systems without static magnetism. We discuss a heuristic model involving percolation of these nanoscale islands with static magnetism as a possible picture to reconcile heterogeneity found by the present MuSR study and long-range spin correlations found by neutron scattering.Comment: 19 pages, 15 figures, submitted to Phys. Rev. B. E-mail: [email protected]

Low Q^2 Jet Production at HERA and Virtual Photon Structure

The transition between photoproduction and deep-inelastic scattering is investigated in jet production at the HERA ep collider, using data collected by the H1 experiment. Measurements of the differential inclusive jet cross-sections dsigep/dEt* and dsigmep/deta*, where Et* and eta* are the transverse energy and the pseudorapidity of the jets in the virtual photon-proton centre of mass frame, are presented for 0 < Q2 < 49 GeV2 and 0.3 < y < 0.6. The interpretation of the results in terms of the structure of the virtual photon is discussed. The data are best described by QCD calculations which include a partonic structure of the virtual photon that evolves with Q2.Comment: 20 pages, 5 Figure

Energy Flow in the Hadronic Final State of Diffractive and Non-Diffractive Deep-Inelastic Scattering at HERA

An investigation of the hadronic final state in diffractive and non--diffractive deep--inelastic electron--proton scattering at HERA is presented, where diffractive data are selected experimentally by demanding a large gap in pseudo --rapidity around the proton remnant direction. The transverse energy flow in the hadronic final state is evaluated using a set of estimators which quantify topological properties. Using available Monte Carlo QCD calculations, it is demonstrated that the final state in diffractive DIS exhibits the features expected if the interaction is interpreted as the scattering of an electron off a current quark with associated effects of perturbative QCD. A model in which deep--inelastic diffraction is taken to be the exchange of a pomeron with partonic structure is found to reproduce the measurements well. Models for deep--inelastic $ep$ scattering, in which a sizeable diffractive contribution is present because of non--perturbative effects in the production of the hadronic final state, reproduce the general tendencies of the data but in all give a worse description.Comment: 22 pages, latex, 6 Figures appended as uuencoded fil

A Search for Selectrons and Squarks at HERA

Data from electron-proton collisions at a center-of-mass energy of 300 GeV are used for a search for selectrons and squarks within the framework of the minimal supersymmetric model. The decays of selectrons and squarks into the lightest supersymmetric particle lead to final states with an electron and hadrons accompanied by large missing energy and transverse momentum. No signal is found and new bounds on the existence of these particles are derived. At 95% confidence level the excluded region extends to 65 GeV for selectron and squark masses, and to 40 GeV for the mass of the lightest supersymmetric particle.Comment: 13 pages, latex, 6 Figure