17 research outputs found
Superconducting transitions from the pseudogap state: d-wave symmetry, lattice, and low-dimensional effects
We investigate the behavior of the superconducting transition temperature
within a previously developed BCS-Bose Einstein crossover picture. This
picture, based on a decoupling scheme of Kadanoff and Martin, further extended
by Patton, can be used to derive a simple form for the superconducting
transition temperature in the presence of a pseudogap. We extend previous work
which addressed the case of s-wave pairing in jellium, to explore the solutions
for T_c as a function of variable coupling in more physically relevant
situations. We thereby ascertain the effects of reduced dimensionality,
periodic lattices and a d-wave pairing interaction. Implications for the
cuprate superconductors are discussed.Comment: REVTeX, 11 pages, 6 EPS figures included, Replace with published
versio
Superconductivity and Density Wave in the Quasi-One-Dimensional Systems: Renormalization Group Study
The anisotropic superconductivity and the density wave have been investigated
by applying the Kadanoff-Wilson renormalization group technique to the
quasi-one-dimensional system with finite-range interactions. It is found that a
temperature (T) dependence of response functions is proportional to exp(1/T) in
a wide region of temperature even within the one-loop approximation. Transition
temperatures are calculated to obtain the phase diagram of the
quasi-one-dimensional system, which is compared with that of the
pure-one-dimensional system. Next-nearest neighbor interactions (V_2) induce
large charge fluctuations, which suppress the d_{x^2 -y^2}-wave singlet
superconducting (dSS) state and enhance the f-wave triplet superconducting
(fTS) state. From this effect, the transition temperature of fTS becomes
comparable to that of dSS for large V_2, so that field-induced f-wave triplet
pairing could be possible. These features are discussed to comprehend the
experiments on the (TMTSF)_2PF_6 salt.Comment: 8 pages, 4 figures, submitted to J. Phys. Soc. Jp
Ginzburg-Landau theory of superconductors with short coherence length
We consider Fermions in two dimensions with an attractive interaction in the
singlet d-wave channel of arbitrary strength. By means of a
Hubbard-Stratonovich transformation a statistical Ginzburg-Landau theory is
derived, which describes the smooth crossover from a weak-coupling BCS
superconductor to a condensate of composite Bosons. Adjusting the interaction
strength to the observed slope of H_c2 at T_c in the optimally doped high-T_c
compounds YBCO and BSCCO, we determine the associated values of the
Ginzburg-Landau correlation length xi and the London penetration depth lambda.
The resulting dimensionless ratio k_F xi(0) approx 5-8 and the Ginzburg-Landau
parameter kappa=lambda xi approx 90-100 agree well with the experimentally
observed values. These parameters indicate that the optimally doped materials
are still on the weak coupling side of the crossover to a Bose regime.Comment: 12 pages, RevTeX, 6 postscript figures, resubmitted with minor
changes in section III, to appear in Physical Review
Pseudogap and Superconducting Fluctuation in High-Tc Cuprates: Theory beyond 1-loop Approximation
The pseudogap phenomena induced by the SC fluctuation are investigated in
details. We perform a calculation beyond the 1-loop approximation. The SC
fluctuation is microscopically derived on the basis of the repulsive Hubbard
model. The vertex corrections are collected in the infinite order with use of
the quasi-static approximation. The single-particle excitations, NMR 1/T_{1}T,
spin susceptibility and superconducting transition temperature are discussed.
The important role of the vertex correction is pointed out for the single
particle spectral function. On the other hand, the validity of the 1-loop order
theory is confirmed for other quantities. We shed light on the essential nature
of SC fluctuation leading to the pseudogap from the comparison with spin and
charge fluctuations
Nonperturbative XY-model approach to strong coupling superconductivity in two and three dimensions
For an electron gas with delta-function attraction we investigate the
crossover from weak- to strong-coupling supercoductivity in two and three
dimensions. We derive analytic expressions for the stiffness of phase
fluctuations and set up effective XY-models which serve to determine
nonperturbatively the temperature of phase decoherence where superconductivity
breaks down. We find the transition temperature T_c as a monotonous function of
the coupling strength and carrier density both in two and three dimensions, and
give analytic formulas for the merging of the temperature of phase decoherence
with the temperature of pair formation in the weak-coupling limit.Comment: Few typos corrected. Emails that were sent to the address
[email protected] in June and July 1999 were lost in a computer crash, so if
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