53 research outputs found
Optical conductivity of metal nanofilms and nanowires: The rectangular-box model
The conductivity tensor is introduced for the low-dimensional electron
systems. Within the particle-in-a-box model and the diagonal response
approximation, components of the conductivity tensor for a quasi-homogeneous
ultrathin metal film and wire are calculated under the assumption (where is the characteristic small dimension of the
system, is the Fermi wavelength for bulk metal). We find the
transmittance of ultrathin films and compare these results with available
experimental data. The analytical estimations for the size dependence of the
Fermi level are presented, and the oscillations of the Fermi energy in
ultrathin films and wires are computed. Our results demonstrate the strong size
and frequency dependences of the real and imaginary parts of the conductivity
components in the infrared range. A sharp distinction of the results for Au and
Pb is observed and explained by the difference in the relaxation time of these
metals.Comment: 13 pages, 8 figure
Vortex phases in mesoscopic cylinders with suppressed surface superconductivity
Vortex structures in mesoscopic cylinder placed in external magnetic field
are studied under the general de Gennes boundary condition for the order
parameter corresponding to the suppression of surface superconductivity. The
Ginzburg-Landau equations are solved based on trial functions for the order
parameter for vortex-free, single-vortex, multivortex, and giant vortex phases.
The equilibrium vortex diagrams in the plane of external field and cylinder
radius and magnetization curves are calculated at different values of de Gennes
"extrapolation length" characterizing the boundary condition for the order
parameter. The comparison of the obtained variational results with some
available exact solutions shows good accuracy of our approach.Comment: RevTex, 11 pages, 10 figure
Effects of broadening and electron overheating in tunnel structures based on metallic clusters
We study the influence of energy levels broadening and electron subsystem
overheating in island electrode (cluster) on current-voltage characteristics of
three-electrode structure. A calculation scheme for broadening effect in
one-dimensional case is suggested. Estimation of broadening is performed for
electron levels in disc-like and spherical gold clusters. Within the
two-temperature model of metallic cluster and by using a size dependence of the
Debye frequency the effective electron temperature as a function of bias
voltage is found approximately. We suggest that the effects of broadening and
electron overheating are responsible for the strong smoothing of
current-voltage curves, which is observed experimentally at low temperatures in
structures based on clusters consisting of accountable number of atoms.Comment: 8 pages, 5 figure
Thermal suppression of surface barrier in ultrasmall superconducting structures
In the recent experiment by Cren \textit{et al.} [Phys. Rev. Lett.
\textbf{102}, 127005 (2009)], no hysteresis for vortex penetration and
expulsion from the nano-island of Pb was observed. In the present paper, we
argue that this effect can be associated with the thermoactivated surmounting
of the surface barrier by a vortex. The typical entrance (exit) time is found
analytically from the Fokker-Planck equation, written in the form suitable for
the extreme vortex confinement. We show that this time is several orders of
magnitude smaller than 1 second under the conditions of the experiment
considered. Our results thus demonstrate a possibility for the thermal
suppression of the surface barrier in nanosized low- superconductors. We
also briefly discuss other recent experiments on vortices in related
structures.Comment: 12 pages, 2 figure
Density-functional theory of elastically deformed finite metallic system: work function and surface stress
The effect of external strain on surface properties of simple metals is
considered within the modified stabilized jellium model. The equations for the
stabilization energy of the deformed Wigner-Seitz cells are derived as a
function of the bulk electron density and the given deformation. The results
for surface stress and work function of aluminium calculated within the
self-consistent Kohn-Sham method are also given. The problem of anisotropy of
the work function of finite system is discussed. A clear explanation of
independent experiments on stress-induced contact potential difference at metal
surfaces is presented.Comment: 15 pages, 1 figur
Approximate Ginzburg-Landau solution for the regular flux-line lattice. Circular cell method
A variational model is proposed to describe the magnetic properties of
type-II superconductors in the entire field range between and
for any values of the Ginzburg-Landau parameter . The
hexagonal unit cell of the triangular flux-line lattice is replaced by a circle
of the same area, and the periodic solutions to the Ginzburg-Landau equations
within this cell are approximated by rotationally symmetric solutions. The
Ginzburg-Landau equations are solved by a trial function for the order
parameter. The calculated spatial distributions of the order parameter and the
magnetic field are compared with the corresponding distributions obtained by
numerical solution of the Ginzburg-Landau equations. The comparison reveals
good agreement with an accuracy of a few percent for all values
exceeding . The model can be extended to anisotropic
superconductors when the vortices are directed along one of the principal axes.
The reversible magnetization curve is calculated and an analytical formula for
the magnetization is proposed. At low fields, the theory reduces to the London
approach at , provided that the exact value of is used.
At high fields, our model reproduces the main features of the well-known
Abrikosov theory. The magnetic field dependences of the reversible
magnetization found numerically and by our variational method practically
coincide. The model also refines the limits of some approximations which have
been widely used. The calculated magnetization curves are in a good agreement
with experimental data on high-T superconductors.Comment: 8 pages, RevTex, 6 figures, submitted to Phys. Rev.
Three-dimensional Ginzburg-Landau simulation of a vortex line displaced by a zigzag of pinning spheres
A vortex line is shaped by a zigzag of pinning centers and we study here how
far the stretched vortex line is able to follow this path. The pinning center
is described by an insulating sphere of coherence length size such that in its
surface the de Gennes boundary condition applies. We calculate the free energy
density of this system in the framework of the Ginzburg-Landau theory and study
the critical displacement beyond which the vortex line is detached from the
pinning center.Comment: Submitted to special issue of Prammna-Journal of Physics devoted to
the Vortex State Studie
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