11 research outputs found
Poor screening and nonadiabatic superconductivity in correlated systems
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 - phase
diagram of cuprates. Experimental evidences are also discussed.Comment: 12 Pages, 6 Figures, Accepted on Physical Review
Upper critical field calculations for the high critical temperature superconductors considering inhomogeneities
We perform calculations to obtain the 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
. The transition to a coherent superconducting phase at a critical
temperature corresponds to a percolation threshold among different
superconducting regions, each one characterized by a given .
Within this model we calculate the upper critical field by means of an
average linearized Ginzburg-Landau (GL) equation to take into account the
distribution of local superconducting temperatures . This
approach explains some of the anomalies associated with and why
several properties like the Meissner and Nernst effects are detected at
temperatures much higher than .Comment: Latex text, add reference
Upper critical field for underdoped high-T_c superconductors. Pseudogap and stripe--phase
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
. 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
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