420 research outputs found
Fluctuating order parameter in doped cuprate superconductors
We discuss static fluctuations of the d-wave superconducting order parameter
in CuO planes, due to quasiparticle scattering by charged dopants.
The analysis of two-particle anomalous Green functions at permits to
estimate the mean-square fluctuation ,
averaged in random dopant configurations, to the lowest order in doping level
. Since is found to saturate with growing doping level while
remains to grow, this can explain the collapse of at overdoping.
Also we consider the spatial correlations for
order parameter in different points of the plane.Comment: RevTex4, 3 pages, to be published in Proceedings of New3SC-4
International Conference, San Diego, California, January 15-21, 200
Superconductivity and superconducting order parameter phase fluctuations in a weakly doped antiferromagnet
The superconducting properties of a recently proposed phenomenological model
for a weakly doped antiferromagnet are analyzed, taking into account
fluctuations of the phase of the order parameter. In this model, we assume that
the doped charge carriers can't move out of the antiferromagnetic sublattice
they were introduced. This case corresponds to the free carrier spectra with
the maximum at , as it was observed in ARPES
experiments in some of the cuprates in the insulating state [1]. The doping
dependence of the superconducting gap and the temperature-carrier density phase
diagram of the model are studied in the case of the pairing
symmetry and different values of the effective coupling. A possible relevance
of the results to the experiments on high-temperature superconductors is
discussed.Comment: 16 pages, 4 figure
Pseudogap phase formation in the crossover from Bose-Einstein condensation to BCS superconductivity in low dimensional systems
A phase diagram for a 2D metal with variable carrier density has been studied
using the modulus-phase representation for the order parameter in a fully
microscopic treatment. This amounts to splitting the degrees of freedom into
neutral fermion and charged boson degrees of freedom. Although true long range
order is forbidden in two dimensions, long range order for the neutral fermions
is possible since this does not violate any continuous symmetry. The phase
fluctuations associated with the charged degrees of freedom destroy long range
order in the full system as expected. The presence of the neutral order
parameter gives rise to new features in the superconducting condensate
formation in low dimensional systems. The resulting phase diagram contains a
new phase which lies above the superconducting (here
Berezinskii-Kosterlitz-Thouless) phase and below the normal (Fermi-liquid)
phase. We identify this phase with the pseudogap phase observed in underdoped
high- superconducting compounds above their critical temperature. We
also find that the phase diagram persists even in the presence of weak
3-dimensionalisation.Comment: 4 pages, LaTeX; invited paper presented at New^3SC-1, Baton Rouge,
USA, 1998. To be published in Int.J.Mod.Phys.
On temperature versus doping phase diagram of high critiical temperature superconductors
The attempt to describe the bell-shape dependence of the critical temperature
of high- superconductors on charge carriers density is made. Its linear
increase in the region of small densities (underdoped regime) is proposed to
explain by the role of the order parameter phase 2D fluctuations which become
less at this density growth. The critical temperature suppression in the region
of large carrier densities (overdoped regime) is connected with the appearance
(because of doping) of the essential damping of long-wave bosons which in the
frame of the model proposed define the mechanism of indirect inter-fermion
attraction.Comment: 15 pages, 3 figures, EMTE
On orientational relief of inter-molecular potential and the structure of domain walls in fullerite C60
A simple planar model for an orientational ordering of threefold molecules on
a triangular lattice modelling a close-packed (111) plane of fullerite is
considered. The system has 3-sublattice ordered ground state which includes 3
different molecular orientations. There exist 6 kinds of orientational domains,
which are related with a permutation or a mirror symmetry. Interdomain walls
are found to be rather narrow.
The model molecules have two-well orientational potential profiles, which are
slightly effected by a presence of a straight domain wall. The reason is a
stronger correlation between neighbour molecules in triangular lattice versus
previously considered square lattice
A considerable reduction (up to one order) of orientational interwell
potential barrier is found in the core regions of essentially two-dimentional
potential defects, such as a three-domain boundary or a kink in the domain
wall. For ultimately uncorrelated nearest neighbours the height of the
interwell barrier can be reduced even by a factor of 100.Comment: 11 pages, 13 figures, LaTeX, to appear in Low Temperature Physic
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