Stripe Phase Of Cuprates Research Articles

Cell dynamics simulations of coupled charge and magnetic phase transformation in correlated oxides.

We present a comprehensive numerical study on the kinetics of phase transition that is characterized by two nonconserved scalar order parameters coupled by a special linear-quadratic interaction. This particular Ginzburg-Landau theory has been proposed to describe the coupled charge and magnetic transition in nickelates and the collinear stripe phase in cuprates. The inhomogeneous state of such systems at low temperatures consists of magnetic domains separated by quasimetallic domain walls where the charge order is reduced. By performing large-scale cell dynamics simulations, we find a two-stage phase-ordering process in which a short period of independent evolution of the two order parameters is followed by a correlated coarsening process. The long-time growth and coarsening of magnetic domains is shown to follow the Allen-Cahn power law. We further show that the nucleation-and-growth dynamics during phase transformation to the ordered states is well described by the Kolmogorov-Johnson-Mehl-Avrami theory in two dimensions. On the other hand, the presence of quasimetallic magnetic domain walls in the ordered states gives rise to a very different kinetics for transformation to the high-temperature paramagnetic phase. In this scenario, the phase transformation is initiated by the decay of magnetic domain walls into two insulator-metal boundaries, which subsequently move away from each other. Implications of our findings to recent nano-imaging experiments on nickelates are also discussed.

Cooperative coupling of static magnetism and bulk superconductivity in the stripe phase of La2−xBaxCuO4 : Pressure- and doping-dependent studies

Static spin-stripe order and superconductivity were systematically studied in La_2-xBa_xCuO_4 (0.11 - 0.17) at ambient pressure by means of magnetization and muSR experiments. We find that all the investigated La_2-xBa_xCuO_4 samples exhibit static spin-stripe order and that the quasi two-dimensional superconducting (SC) transition temperature T_c1 and the static spin-stripe order temperature T_so have very similar values throughout the phase diagram. Moreover, the magnetic and the SC properties of the x = 0.155 (LBCO-0.155) and x = 0.17 (LBCO-0.17) samples were studied under hydrostatic pressure. As a remarkable result, in these bulk cuprate superconductors the three-dimensional SC transition temperature T_c and T_so nearly coincide at all pressure investigated (0 - 2.3 GPa). We also observed a pressure induced transition from long-range spin stripe order to a disordered magnetic state at 1.6 GPa in LBCO-0.155, coexisting with a SC state with substantial superfluid density. In LBCO-0.17 a disordered magnetic state is present at all p. The present results indicate that static magnetic order and SC pairing correlations develop in a cooperative fashion in La_2-xBa_xCuO_4, and provide a new route of understanding the complex interplay between static magnetism and superconductivity in the stripe phase of cuprates.

Oxygen isotope effects on lattice properties ofLa2−xBaxCuO4(x=1/8)

A novel negative oxygen-isotope (16O/18O) effect (OIE) on the low-temperature tetragonal phase transition temperature T_{LTT} was observed in La_{2-x}Ba_xCuO_4 (x = 1/8) using high-resolution neutron powder diffraction. The corresponding OIE exponent alpha(T_{LTT}) = - 0.36(5) has the same sign as alpha(T_{so}) = -0.57(6) found for the spin-stripe order temperature T_so. The fact that the LTT transition is accompanied by charge ordering (CO) implies the presence of an OIE also for the CO temperature T_co. Furthermore, a temperature dependent shortening of the c-axis with the heavier isotope is observed. These results combined with model calculations demonstrate that anharmonic electron-lattice interactions are essential for all transitions observed in the stripe phase of cuprates.

Feshbach resonance and mesoscopic phase separation near a quantum critical point inmultiband FeAs-based superconductors

High-Tc superconductivity in FeAs-based (pnictide) multilayers, evading temperature decoherenceeffects in a quantum condensate, is assigned to a Feshbach resonance (also called shaperesonance) in the exchange-like interband pairing. The resonance is switched on by tuningthe chemical potential at an electronic topological transition (ETT) near a bandedge, where the Fermi surface topology of one of the subbands changes fromone-dimensional (1D) to two-dimensional (2D) topology. We show that the tuningis realized by changing (i) the misfit strain between the superconducting planesand the spacers, (ii) the charge density, and (iii) the disorder. The system is atthe verge of a catastrophe, i.e. near a structural and magnetic phase transitionassociated with the order-to-disorder phase transition of the stripes (analogous to the1/8 stripephase in cuprates). Fine tuning of both the chemical potential and the disorder pushes the criticaltemperature Ts of this phase transition to zero, giving a quantum critical point. Here the quantum latticeand magnetic fluctuations promote the Feshbach resonance of the exchange-like anisotropicpairing. This superconducting phase that resists the attacks of temperature is shown to becontrolled by the interplay of the hopping energy between stripes and the quantumfluctuations. The superconducting gaps in the multiple Fermi surface spots reported by therecent ARPES experiment of Evtushinsky et al (2008 arXiv: 0809.4455) are shown tosupport the Feshbach scenario.

Harmonic peaks of stripe phases in cuprates

We calculate the relative intensities of the main incommensurate and third harmonic peaks expected from elastic neutron scattering for various stripe phases observed in nickelates and some cuprate superconductors. We consider vertical and diagonal stripes and compare both site- and bond-centered configurations of the domain walls. Upon comparing the calculated ratio of the main incommensurate peaks to the next harmonic peaks in these configurations to the background and errors in neutron scattering experiments, we conclude that in most cases in the cuprates, the harmonic peaks expected from stripes are too weak to be detected.

Dynamic properties of inhomogeneous states in cuprates (Review Article)

We review the static and dynamical properties of stripe textures with regard to their relevance in high-Tc superconductors. Our investigations are based on the time-dependent Gutzwiller approximation which allows for the computation of random-phase approximation-like (RPA) fluctuations on top of the Gutzwiller approximation (GA). No restrictions are imposed on the charge and spin configurations, which makes the method suitable for the calculation of linear excitations around symmetry-broken solutions. Within this approach we calculate the optical conductivity of stripes and compare our results with reflectivity experiments on cuprates. Further on, we use the spin-rotational invariant extension of the GA+RPA method in order to investigate the characteristics of magnetic excitations in the stripe phase of cuprates. Our results are in very good agreement with neutron scattering and optical experiments on lanthanum cuprate superconductors.

Doping induced crossover between site‐centered stripe phase and bond‐centered stripe phase of cuprates

AbstractUsing a combination of the bond formalism with the recursion method of calculating the Green's function of hole moving in the antiferromagnet (AF) spin 1/2 background we evaluate the energy of a single bond‐centered, bond‐ordered stripe and compare with the energy of a site‐centered stripe. By taking into account the width change of AF domains separated by hole‐rich domain walls (DWs) we find that the crossover between the phase of site‐centered stripes and the phase of bond‐centered stripes takes place upon doping the 2D spin 1/2 AF. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Stripes, vibrations, and superconductivity

We propose a model of a spatially modulated collective charge state of superconducting cuprates. The regions of higher carrier density (stripes) are described in terms of Luttinger liquids and the regions of lower density as a two-dimensional interacting bosonic gas of d_{x^2-y^2} hole pairs. The interactions among the elementary excitations are repulsive and the transition to the superconducting state is driven by decay processes. Vibrations of the CCS and the lattice, although not participating directly in the binding mechanism, are fundamental for superconductivity. The superfluid density and the lattice have a strong tendency to modulation implying a still unobserved dimerized stripe phase in cuprates. The phase diagram of the model has a crossover from 1D to 2D behavior and a pseudogap region where the amplitude of the order parameters are finite but phase coherence is not established. We discuss the nature of the spin fluctuations and the unusual isotope effect within the model.

Vanishing Hall constant in the stripe phase of cuprates

The Hall constant ${R}_{H}$ is considered for the stripe structures. In order to explain the vanishing of ${R}_{H}$ in ${\mathrm{La}}_{2\ensuremath{-}y\ensuremath{-}x}{\mathrm{Nd}}_{y}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ at $x=\frac{1}{8},$ we use the relation of ${R}_{H}$ to the Drude weight D as well as direct numerical calculation to obtain results within the $t\ensuremath{-}J$ model, where the stripes are imposed via a charge potential and a staggered magnetic field. The origin of ${R}_{H}\ensuremath{\sim}0$ is related to a maximum in D and the minimal kinetic energy in stripes with a hole filling $\ensuremath{\sim}\frac{1}{2}.$ The same argument indicates a possibility of ${R}_{H}\ensuremath{\sim}0$ in the whole range of static stripes for $x<~\frac{1}{8}.$

Stripe dynamics, global phase ordering, and quantum criticality in high-Tcsuperconductors

By modeling the stripe phase in cuprates as spin gapped stripes coupled to the RVB liquid of preformed electron pairs, I derive the low energy effective theory of the RVB phase variable. It is found that the effect of stripe dynamics (including both longitudinal and transverse modes) leads to incipient temporal phase stiffness in the RVB liquid, which tunes a quantum phase transition toward a superconducting ground state with global phase order. Physical consequences of this quantum criticality are discussed.

Landau theory of stripe phases in cuprates and nickelates

We consider a Landau theory of coupled charge and spin-density wave order parameters as a simple model for the ordering that has been observed experimentally in the La_2NiO_4 and La_2CuO_4 families of doped antiferromagnets. The period of the charge-density wave is generically half that of the spin-density wave, or equivalently the charges form antiphase domain walls in the antiferromagnetic order. A sharp distinction exists between the case in which the ordering is primarily charge driven (which produces a sequence of transitions in qualitative agreement with experiment) or spin driven (which does not). We also find that stripes with non-collinear spin order (i.e. spiral phases) are possible in a region of the phase diagram where the transition is spin driven; the spiral is circular only when there is no charge order, and is otherwise elliptical with an eccentricity proportional to the magnitude of the charge order.