762 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
Superconducting junctions from non-superconducting doped CuO layers
The theoretical approach proposed recently for description of redistribution
of electronic charge in multilayered selectively doped systems is modified for
a system with finite number of layers. A special attention is payed to the case
of a finite heterostructure made of copper-oxide layers which are all
non-superconducting (including non-conducting) because of doping levels being
beyond the well-known characteristic interval for superconductivity. Specific
finite structures and doping configurations are proposed to obtain atomically
thin superconducting heterojunctions of different compositions.Comment: 4 pages, 3 figures, two bibliography references were update
Boundary Friction on Molecular Lubricants: Rolling Mode?
A theoretical model is proposed for low temperature friction between two
smooth rigid solid surfaces separated by lubricant molecules, admitting their
deformations and rotations. Appearance of different modes of energy dissipation
(by ''rocking'' or ''rolling'' of lubricants) at slow relative displacement of
the surfaces is shown to be accompanied by the stick-and-slip features and
reveals a non-monotonic (mean) friction force {\it vs} external loadComment: revtex4, 4 pages, 5 figure
Group expansions for impurities in superconductors
A new method is proposed for practical calculation of the effective
interaction between impurity scatterers in superconductors, based on algebraic
properties of related Nambu matrices for Green functions. In particular, we
show that the density of states within the s-wave gap can have a non-zero
contribution (impossible either in Born and in T-matrix approximation) from
non-magnetic impurities with concentration , beginning from order.Comment: 5 pages, 1 figur
On the theory of high- superconductivity of doped cuprates
A theoretical analysis is presented on possible effects of disorder by
dopants in high-temperature superconducting cuprate perovskites, to define
their basic spectra of spin and electronic excitations, and the subsequent
observable properties, especially doping dependence of superconducting order
parameter. The central point in the proposed physical picture is formation of
specific impurity subband within the insulating bandgap of initial undoped
material, serving as a source for the system metallization and further
transition into superconducting state with anisotropic order parameter.Comment: 20 pages, 11 figure
Low-temperature orientational order and possible domain structures in C(_{60}) fullerite
Based on a simple model for ordering of hexagons on square planar lattice, an
attempt has been made to consider possible structure of C(_{60}) fullerite in
its low temperature phase. It is shown that hexagons, imitating fullerens
oriented along (C_{3}) axes of \emph{sc} lattice, can be ordered into an ideal
structure with four non-equivalent molecules in unit cell. Then the energy
degeneracy for each hexagon rotations by (\pi /3) around its (C_{3}) axis
leaves the translational and orientational order in this structure, but leads
to a random distribution of (\pi /3) rotations and hence to {}``averaged{}''
unit cell with two molecules. However the most relevant structural defects are
not these intrinsic \char`\"{}misorientations\char`\"{} but certain walls
between the domains with different sequencies of the above-mentioned two
(non-ideal) sublattices. Numeric estimates have been made for the anisotropic
inter-molecular potential showing that the anisotropy is noticeably smaller for
molecules in walls than in domains
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