162 research outputs found
The Inner Life of the Kondo Ground State: An Answer to Kenneth Wilson's Question
The Kondo ground state has been investigated by numerical and exact methods,
but the physics behind these results remains veiled. Nobel prize winner Wilson,
who engineered the break through in his numerical renormalization group theory,
commented in his review article "the author has no simple explanation ...for
the crossover from weak to strong coupling". In this article a graphical
interpretation is given for the extraordinary properties of the Kondo ground
state. At the crossover all electron states in the low energy range of
k_{B}T_{K} are synchronized. An internal orthogonality catastrophe is averted.Comment: 4 figure
Induced Spin-Currents in Alkali-Films
In sandwiches of FeK and FeCs the conduction electrons in the alkali metals
have a large mean free path. The experiments suggest that the specular
reflection for spin up and down electrons is different at the interface
yielding a spin current in the alkali film. The spin current is detected by the
anomalous Hall effect of Pb surface impurities
The Conductance of a Perfect Thin Film with Diffuse Surface Scattering
The conductance of thin films with diffusive surface scattering was solved
semi-classically by Fuchs and Sondheimer. However, when the intrinsic electron
mean free path is very large or infinite their conductance diverges. In this
letter a simple diffraction picture is presented. It yields a conductance which
corresponds to a limiting mean free path. PACS: 73.50.-h, 73.50.Bk, 73.23.-b,
73.25.+i, B14
The Meservey-Tedrov effect in FSF double tunneling junctions
Double tunneling junctions of ferromagnet-superconductor-ferromagnet
electrodes (FSF) show a jump in the conductance when a parallel magnetic field
reverses the magnetization of one of the ferromagnetic electrodes. This change
is generally attributed to the spin-valve effect or to pair breaking in the
superconductor because of spin accumulation. In this paper it is shown that the
Meservey-Tedrov effect causes a similar change in the conductance since the
magnetic field changes the energy spectrum of the quasi-particles in the
superconductor. A reversal of the bias reverses the sign in the conductance
jump
Quantitative Simulation of the Superconducting Proximity Effect
A numerical method is developed to calculate the transition temperature of
double or multi-layers consisting of films of super- and normal conductors. The
approach is based on a dynamic interpretation of Gorkov's linear gap equation
and is very flexible. The mean free path of the different metals, transmission
through the interface, ratio of specular reflection to diffusive scattering at
the surfaces, and fraction of diffusive scattering at the interface can be
included. Furthermore it is possible to vary the mean free path and the BCS
interaction NV in the vicinity of the interface. The numerical results show
that the normalized initial slope of an SN double layer is independent of
almost all film parameters except the ratio of the density of states. There are
only very few experimental investigations of this initial slope and they
consist of Pb/Nn double layers (Nn stands for a normal metal). Surprisingly the
coefficient of the initial slope in these experiments is of the order or less
than 2 while the (weak coupling) theory predicts a value of about 4.5. This
discrepancy has not been recognized in the past. The autor suggests that it is
due to strong coupling behavior of Pb in the double layers. The strong coupling
gap equation is evaluated in the thin film limit and yields the value of 1.6
for the coefficient. This agrees much better with the few experimental results
that are available.
PACS: 74.45.+r, 74.62.-c, 74.20.F
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