Manifestation of marginal Fermi liquid and phonon excitations in photoemision experiments of cuprate superconductors

Recent ARPES experiments in cuprates superconductors show a kink in the electron dispersion near the Fermi energy. This kink coexists with a linear frequency dependence of the imaginary part of the electron self-energy. In this paper we show that both features could be accounted for if an electron-phonon interaction is included in a model where the electrons are described by a marginal Fermi liquid theory. Phonons provide the energy scale seen in the experiments but the quasiparticle weight at the Fermi level is zero. At high binding energy, in agreement with the experiment, the electron dispersion does not go to the one-electron band. We analyze the compatibility between the electron scattering rate extracted from ARPES experiment and the one extracted from transport properties. We conclude that the electron-phonon interaction relevant for transport properties is strongly screened respect to the one extracted from ARPES. This is in agreement with recent studies in the context of 1/N expansion on t-J model.Comment: 5 pages, latex, 3 figures embedded in the tex

Influence of collective effects and the d-CDW on electronic Raman scattering in high-Tc_c superconductors

Electronic Raman scattering in high-T$_c$ superconductors is studied within the t-J model. It is shown that the A$_{1g}$ and B$_{1g}$ spectra are dominated by amplitude fluctuations of the superconducting and the d-wave CDW order parameters, respectively. The B$_{2g}$ spectrum contains no collective effects and its broad peak reflects vaguely the doping dependence of T$_c$, similarly to the pronounced peak in the A$_{1g}$ spectrum. The agreement of our theory with the experiment supports the picture of two different, competing order parameters in the underdoped regime of high-T$_c$ superconductors.Comment: 4 pages, 4 figures, will appear in PR

Collective excitations in unconventional charge-density wave systems

The excitation spectrum of the t-J model is studied on a square lattice in the large $N$ limit in a doping range where a $d$-$density$-$wave$ (DDW) forms below a transition temperature $T^\star$. Characteristic features of the DDW ground state are circulating currents which fluctuate above and condense into a staggered flux state below $T^\star$ and density fluctuations where the electron and the hole are localized at different sites. General expressions for the density response are given both above and below $T^\star$ and applied to Raman, X-ray, and neutron scattering. Numerical results show that the density response is mainly collective in nature consisting of broad, dispersive structures which transform into well-defined peaks mainly at small momentum transfers. One way to detect these excitations is by inelastic neutron scattering at small momentum transfers where the cross section (typically a few per cents of that for spin scattering) is substantially enhanced, exhibits a strong dependence on the direction of the transferred momentum and a well-pronounced peak somewhat below twice the DDW gap. Scattering from the DDW-induced Bragg peak is found to be weaker by two orders of magnitude compared with the momentum-integrated inelastic part.Comment: 10 pages, 8 figure

ING4 (inhibitor of growth family, member 4)

Review on ING4 (inhibitor of growth family, member 4), with data on DNA, on the protein encoded, and where the gene is implicated

Damage identification on spatial Timoshenko arches by means of genetic algorithms

In this paper a procedure for the dynamic identification of damage in spatial Timoshenko arches is presented. The proposed approach is based on the calculation of an arbitrary number of exact eigen-properties of a damaged spatial arch by means of the Wittrick and Williams algorithm. The proposed damage model considers a reduction of the volume in a part of the arch, and is therefore suitable, differently than what is commonly proposed in the main part of the dedicated literature, not only for concentrated cracks but also for diffused damaged zones which may involve a loss of mass. Different damage scenarios can be taken into account with variable location, intensity and extension of the damage as well as number of damaged segments. An optimization procedure, aiming at identifying which damage configuration minimizes the difference between its eigen-properties and a set of measured modal quantities for the structure, is implemented making use of genetic algorithms. In this context, an initial random population of chromosomes, representing different damage distributions along the arch, is forced to evolve towards the fittest solution. Several applications with different, single or multiple, damaged zones and boundary conditions confirm the validity and the applicability of the proposed procedure even in presence of instrumental errors on the measured data.Comment: 34 pages, 19 figure

Effective interactions and superconductivity in the t-J model in the large-N limit

The feasibility of a perturbation expansion for Green's functions of the t-J model directly in terms of X-operators is demonstrated using the Baym- Kadanoff functional method. As an application we derive explicit expressions for the kernel of the linearized equation for the superconducting order parameter in leading order of a 1/N expansion. The linearized equation is solved numerically on a square lattice. We find that a reasonably strong instability occurs only for even frequency pairing with d-wavelike symmetry. Results for the transition temperature and the effective interaction are given as a function of doping.Comment: 31 pages, 11 figure