A Vertex Correction in the Gap Equation for the High Temperature Superconductors

We show that the Migdal theorem is obviously violated in the high Tc cuprates and the vertex correction should be included, in particular, in the gap equation, in order to be consistent with the anomalously strong inelastic scattering in the ``hot spots'', which is observed from the various normal state experiments. The vertex correction is obtained by utilizing the generalized Ward identity, which is shown to hold in the important scattering channel for the pairing interaction in the high Tc cuprates. As a result, we find a strong enhancement of Tc from the vertex correction despite of the strong pair breaking effect due to the inelastic scattering.Comment: 5 pages, 2 figure

Nanovesicles loaded with origanum onites and satureja thymbra essential oils and their activity against food-borne pathogens and spoilage microorganisms

Food poisoning is a common cause of illness and death in developing countries. Essential oils (EOs) could be effective and safe natural preservatives to prevent and control bacterial contamination of foods. However, their high sensitivity and strong flavor limit their application and biological effectiveness. The aim of this study was firstly the chemical analysis and the antimicrobial evaluation of the EOs of Origanum onites L. and Satureja thymbra L. obtained from Symi island (Greece), and, secondly, the formulation of propylene glycol-nanovesicles loaded with these EOs to improve their antimicrobial properties. The EOs were analyzed by GC-MS and their chemical contents are presented herein. Different nanovesicles were formulated with small average sizes, high homogeneity, and optimal ζ-potential. Microscopic observation confirmed their small and spherical shape. Antibacterial and antifungal activities of the formulated EOs were evaluated against food-borne pathogens and spoilage microorganisms compared to pure EOs. Propylene glycol-nanovesicles loaded with O. onites EO were found to be the most active formulation against all tested strains. Additionally, in vitro studies on the HaCaT cell line showed that nanovesicles encapsulated with EOs had no toxic effect. The present study revealed that both EOs can be used as alternative sanitizers and preservatives in the food industry, and that their formulation in nanovesicles can provide a suitable approach as food-grade delivery system

Example of a self-consistent solution for a fermion on domain wall

We discuss a self-consistent solution for a fermion coupled to static scalar field in the form of a kink (domain wall). In particular, we study the case when the fermion occupies an excited non-zero frequency level in the presence of the domain wall field. The effect of the domain wall profile distortion is calculated analytically.Comment: 9 pages, no figures; minor corrections, one reference added, results unchange

Effect of FET geometry on charge ordering of transition metal oxides

We examine the effect of an FET geometry on the charge ordering phase diagram of transition metal oxides using numerical simulations of a semiclassical model including long-range Coulomb fields, resulting in nanoscale pattern formation. We find that the phase diagram is unchanged for insulating layers thicker than approximately twice the magnetic correlation length. For very thin insulating layers, the onset of a charge clump phase is shifted to lower values of the strength of the magnetic dipolar interaction, and intermediate diagonal stripe and geometric phases can be suppressed. Our results indicate that, for sufficiently thick insulating layers, charge injection in an FET geometry can be used to experimentally probe the intrinsic charge ordering phases in these materials.Comment: 4 pages, 4 postscript figure

Stable branches of a solution for a fermion on domain wall

We discuss the case when a fermion occupies an excited non-zero frequency level in the field of domain wall. We demonstrate that a solution exists for the coupling constant in the limited interval $1<g<g_{max}\approx 1.65$. We show that indeed there are different branches of stable solution for $g$ in this interval. The first one corresponds to a fermion located on the domain wall ($1<g<\sqrt[4]{2\pi}$). The second branch, which belongs to the interval $\sqrt[4]{2\pi}\le g\le g_{max}$, describes a polarized fermion off the domain wall. The third branch with $1<g<g_{max}$ describes an excited antifermion in the field of the domain wall.Comment: 15 pages, 7 figures, references adde

Strong enhancement of spin fluctuations in the low-temperature-tetragonal phase of antiferromagnetically ordered La_{2-x-y}Eu_ySr_xCuO_4

Measurements of the static magnetization, susceptibility and ESR of Gd spin probes have been performed to study the properties of antiferromagnetically ordered La_{2-x-y}Eu_ySr_xCuO_4 (x less or equal 0.02) with the low temperature tetragonal structure. According to the static magnetic measurements the CuO_2 planes are magnetically decoupled in this structural phase. The ESR study reveals strong magnetic fluctuations at the ESR frequency which are not present in the orthorhombic phase. It is argued that this drastic enhancement of the spin fluctuations is due to a considerable weakening of the interlayer exchange and a pronounced influence of hole motion on the antiferromagnetic properties of lightly hole doped La_2CuO_4. No evidence for the stripe phase formation at small hole doping is obtained in the present study.Comment: 10 pages, LaTeX, 3 EPS figures; to be published in Journal of Physics: Condensed Matte

Andreev Bound States and Self-Consistent Gap Functions for SNS and SNSNS Systems

Andreev bound states in clean, ballistic SNS and SNSNS junctions are calculated exactly and by using the Andreev approximation (AA). The AA appears to break down for junctions with transverse dimensions chosen such that the motion in the longitudinal direction is very slow. The doubly degenerate states typical for the traveling waves found in the AA are replaced by two standing waves in the exact treatment and the degeneracy is lifted. A multiple-scattering Green's function formalism is used, from which the states are found through the local density of states. The scattering by the interfaces in any layered system of ballistic normal metals and clean superconducting materials is taken into account exactly. The formalism allows, in addition, for a self-consistent determination of the gap function. In the numerical calculations the pairing coupling constant for aluminum is used. Various features of the proximity effect are shown

Crossing the phantom divide with Ricci-like holographic dark energy

We study a holographic model for the dark energy considered recently in the literature which postulates an energy density $\rho \sim R$, where $R$ is the Ricci scalar curvature. We obtain a cosmological scenario that comes from considering two non-interacting fluids along a reasonable Ansatz for the cosmic coincidence parameter. We adjust the involved parameters in the model according to the observational data and we show that the equation of state for the dark energy experience a cross through the -1 barrier. In addition, we find a disagreement in these parameters with respect to an approach from a scalar field theory.Comment: Match with accepted version by EPJ

NMR and Neutron Scattering Experiments on the Cuprate Superconductors: A Critical Re-Examination

We show that it is possible to reconcile NMR and neutron scattering experiments on both LSCO and YBCO, by making use of the Millis-Monien-Pines mean field phenomenological expression for the dynamic spin-spin response function, and reexamining the standard Shastry-Mila-Rice hyperfine Hamiltonian for NMR experiments. The recent neutron scattering results of Aeppli et al on LSCO (x=14%) are shown to agree quantitatively with the NMR measurements of $^{63}T_1$ and the magnetic scaling behavior proposed by Barzykin and Pines. The reconciliation of the $^{17}T_1$ relaxation rates with the degree of incommensuration in the spin fluctuation spectrum seen in neutron experiments is achieved by introducing a new transferred hyperfine coupling $C'$ between oxygen nuclei and their next nearest neighbor $Cu^{2+}$ spins; this leads to a near-perfect cancellation of the influence of the incommensurate spin fluctuation peaks on the oxygen relaxation rates of LSCO. The inclusion of the new $C'$ term also leads to a natural explanation, within the one-component model, the different temperature dependence of the anisotropic oxygen relaxation rates for different field orientations, recently observed by Martindale $et~al$. The measured significant decrease with doping of the anisotropy ratio, $R= ^{63}T_{1ab}/^{63}T_{1c}$ in LSCO system, from $R =3.9$ for ${\rm La_2CuO_4}$ to $R ~ 3.0$ for LSCO (x=15%) is made compatible with the doping dependence of the shift in the incommensurate spin fluctuation peaks measured in neutron experiments, by suitable choices of the direct and transferred hyperfine coupling constants $A_{\beta}$ and B.Comment: 24 pages in RevTex, 9 figures include

A Theory of the Longitudinal and Hall Conductivities of the Cuprate Superconductors

We establish the applicability to transport phenomena in the cuprate superconductors of a nearly antiferromagnetic Fermi liquid (NAFL) description of the magnetic interaction between planar quasiparticles by using it to obtain the temperature dependent resistivity and Hall conductivity seen experimentally in the normal state. Following a perturbative calculation of the anisotropic (as one goes around the Fermi surface) quasiparticle lifetimes which are the hallmark of a NAFL, we obtain simple approximate expressions for the longitudinal, $\sigma_{xx}$, and Hall, $\sigma_{xy}$, conductivities which reflect the magnetic crossovers seen experimentally as one varies the doping level and temperature. We present a simple phenomenological model for the variation in mean free path around the Fermi surface, and use this to extract from experiments on $\sigma_{xx}$ and $\sigma_{xy}$ quasiparticle lifetimes in the hot (strongly coupled quasiparticle) and cold (weakly coupled quasiparticle) regions of the Fermi surface which are consistent with the perturbation theory estimates. We improve upon the latter by carrying out direct numerical (non-variational) solutions of the Boltzmann equation for representative members of the YBa$_2$Cu$_3$O$_{6+x}$ and La$_{2-x}$Sr$_x$CuO$_4$ systems, with results for transport properties in quantitative agreement with experiment. Using the same numerical approach we study the influence of CuO chains on the a-b plane anisotropy and find results in agreement with experimental findings in YBa$_2$Cu$_4$O$_8$.Comment: 49 pages + 24 PostScript figure