11 research outputs found

    Poor screening and nonadiabatic superconductivity in correlated systems

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    In this paper we investigate the role of the electronic correlation on the hole doping dependence of electron-phonon and superconducting properties of cuprates. We introduce a simple analytical expression for the one-particle Green's function in the presence of electronic correlation and we evaluate the reduction of the screening properties as the electronic correlation increases by approaching half-filling. The poor screening properties play an important role within the context of the nonadiabatic theory of superconductivity. We show that a consistent inclusion of the reduced screening properties in the nonadiabatic theory can account in a natural way for the TcT_c-δ\delta phase diagram of cuprates. Experimental evidences are also discussed.Comment: 12 Pages, 6 Figures, Accepted on Physical Review

    Upper critical field Hc2H_{c2} calculations for the high critical temperature superconductors considering inhomogeneities

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    We perform calculations to obtain the Hc2H_{c2} curve of high temperature superconductors (HTSC). We consider explicitly the fact that the HTSC possess intrinsic inhomogeneities by taking into account a non uniform charge density ρ(r)\rho(r). The transition to a coherent superconducting phase at a critical temperature TcT_c corresponds to a percolation threshold among different superconducting regions, each one characterized by a given Tc(ρ(r))T_c(\rho(r)). Within this model we calculate the upper critical field Hc2H_{c2} by means of an average linearized Ginzburg-Landau (GL) equation to take into account the distribution of local superconducting temperatures Tc(ρ(r))T_c(\rho(r)). This approach explains some of the anomalies associated with Hc2H_{c2} and why several properties like the Meissner and Nernst effects are detected at temperatures much higher than TcT_c.Comment: Latex text, add reference

    Upper critical field for underdoped high-T_c superconductors. Pseudogap and stripe--phase

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    We investigate the upper critical field in a stripe--phase and in the presence of a phenomenological pseudogap. Our results indicate that the formation of stripes affects the Landau orbits and results in an enhancement of Hc2H_{c2}. On the other hand, phenomenologically introduced pseudogap leads to a reduction of the upper critical field. This effect is of particular importance when the magnitude of the gap is of the order of the superconducting transition temperature. We have found that a suppression of the upper critical field takes place also for the gap that originates from the charge--density waves.Comment: 7 pages, 5 figure

    The irreversibility line of overdoped Bi_{2+x}Sr_{2-(x+y)}Cu_{1+y}O_{6 +- delta} at ultra-low temperatures and high magnetic fields

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    The irreversible magnetization of the layered high-T_{c} superconductor Bi_{2+x}Sr_{2-(x+y)}Cu_{1+y}O_{6 +- delta} (Bi-2201) has been measured by means of a capacitive torquemeter up to B=28 T and down to T=60 mK. No magnetization jumps, peak effects or crossovers between different pinning mechanisms appear to be present. The deduced irreversibility field B_{irr} can not be described by the law B_{irr}(T)=B_{irr}(0)(1-T/T_{c})^n based on flux creep, but an excellent agreement is found with the analytical form of the melting line of the flux lattice as calculated from the Lindemann criterion. The behavior of B_{irr}(T) obtained here is very similar to the resistive critical field of a Bi-2201 thin film, suggesting that magnetoresistive experiments are likely to be strongly influenced by flux lattice melting.Comment: 4 pages, 4 eps figure

    Early intervention with high‐risk teenage mothers and their infants

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