5,603 research outputs found
Voltage-controlled Group Velocity of Edge Magnetoplasmon in the Quantum Hall Regime
We investigate the group velocity of edge magnetoplasmons (EMPs) in the
quantum Hall regime by means of time-of-flight measurement. The EMPs are
injected from an Ohmic contact by applying a voltage pulse, and detected at a
quantum point contact by applying another voltage pulse to its gate. We find
that the group velocity of the EMPs traveling along the edge channel defined by
a metallic gate electrode strongly depends on the voltage applied to the gate.
The observed variation of the velocity can be understood to reflect the degree
of screening caused by the metallic gate, which damps the in-plane electric
field and hence reduces the velocity. The degree of screening can be controlled
by changing the distance between the gate and the edge channel with the gate
voltage.Comment: 5 pages, 6 figures, to be published in Physical Review
Transport and triplet superconducting condensate in mesoscopic ferromagnet-superconductor structures
We calculate the conductance of a superconductor/ferromagnet (S/F) mesoscopic
structure in the dirty limit. First we assume that the ferromagnet exhibits a
homogeneous magnetization and consider the case that the penetration of the
condensate into the F wire is negligible and the case in which the proximity
effect is taken into account. It is shown that if the exchange field is large
enough, the conductance below the critical temperature , is always smaller
than the conductance in the normal state. At last, we calculate the conductance
for a F/S structure with a local inhomogeneity of the magnetization in the
ferromagnet. We demonstrate that a triplet component of the condensate is
induced in the F wire.This leads to a increase of the conductance below .Comment: 31 pages, 6 figures. to be published in International Journal of
Modern Physics B; references adde
DNA Torsional Solitons in Presence of localized Inhomogeneities
In the present paper we investigate the influence of inhomogeneities in the
dynamics and stability of DNA open states, modeled as propagating solitons in
the spirit of a Generalized Yakushevish Model. It is a direct consecuence of
our model that there exists a critical distance between the soliton's center of
mass and the inhomogeneity at which the interaction between them can change the
stability of the open state.Furtherly from this results was derived a
renormalized potential funtion.Comment: RevTex, 13 pages, 3 figures, final versio
Density of States in Superconductor - Normal Metal - Superconductor Junctions
We consider the chi_0 dependence of the density of states inside the normal
metal of a superconductor - normal metal - superconductor (SNS) junction.Here
chi_0 is the phase difference of two superconductors of the junction. It is
shown that in the absence of electron-electron interaction the energy
dependence of the density of states has a gap which decreases as chi_0
increases and closes at chi_0= pi. Both the analytical expressions for the
chi_0 dependence of the density of states and the results of numerical
simulations are presented.Comment: 7 pages with 4 included epsf figures, published version with small
change
Resistive transport in a mesoscopic proximity superconductor
We review transport measurements in a normal metal (N) in contact with one or
two superconducting (S) islands. From the experiment, we distinguish the
Josephson coupling, the mesoscopic fluctuations and the proximity effect. In a
loop-shaped N conductor, we observe large h/2e-periodic magnetoresistance
oscillations that decay with temperature T with a 1/T power-law. This behaviour
is the signature of the long-range coherence of the low-energy electron pairs
induced by the Andreev reflection at the S interface. At temperature and
voltage below the Thouless energy , we observe the re-entrance
of the metallic resistance. Experimental results agree with the linearized
quasiclassical theory.Comment: 8 pages, 6 included epsf figures, Invited paper at the LT21
Conference, Praha, August 1996. To appear in Czech. J. of Phys. 46, Part S6
(1996
Calculations of Resonance Coupling Constants in the Scalar Sector of the ENJL Model
We derive the scalar resonance coupling constants of resonance chiral theory
from the Extended Nambu Jona-Lasinio model by using heat-kernel expansion.Comment: 7 page
On the two-photon decay width of the sigma meson
We shortly report on the two-photon decay width of the light -meson
interpreted as a quarkonium state. Results are given in dependence on the
-mass and the constituent mass of the light quark. The triangle
quark-loop diagram, responsible for the two-photon transition, is carefully
evaluated: a term in the transition amplitude, often omitted in literature,
results in destructive interference with the leading term. As a result we show
that the two-photon decay width of the in the quarkonium picture is
less than 1 keV for the physical range of parameters.Comment: 6 pages, 4 figure
Giant Conductance Oscillations In Mesoscopic Andreev Interferometers
We analyze the electrical conductance of a two-dimensional, phase
coherent structure in contact with two superconductors, which is known to be an
oscillatory function of the phase difference between the
superconductors. It is predicted that for a metallic sample, the amplitude of
oscillation is enhanced by placing a normal barrier at the interface and that,
by tuning the strength of the barrier, can be orders of magnitude greater than
values observed in recent experiments. Giant oscillations can also be obtained
without a barrier, provided a crucial sum rule is broken. This can be achieved
by disorder induced normal scattering. In the absence of zero phase
inter-channel scattering, the conductance possesses a zero phase minimum.Comment: 4 pages of Revtex, 6 figures available on reques
Phase coherent transport in hybrid superconducting structures: the case of d-wave superconductors
We examine the effect of d-wave symmetry on zero bias anomalies in
normal-superconducting tunnel junctions and phase-periodic conductances in
Andreev interferometers. In the presence of d-wave pairing, zero-bias anomalies
are suppressed compared with the s-wave case. For Andreev interferometers with
aligned islands, the phase-periodic conductance is insensistive to the nature
of the pairing, whereas for non-aligned islands, the nature of the zero-phase
extremum is reversed.Comment: 10 Pages, Revtex. 11 postscript figures available on reques
Three form potential in (special) minimal supergravity superspace and supermembrane supercurrent
This contribution begins the study of the complete superfield Lagrangian
description of the interacting system of D=4 N=1 supergravity (SUGRA) and
supermembrane. Firstly, we review a 'three form supergravity' by Ovrut and
Waldram, which we prefer to call 'special minimal supergravity'. This off-shell
formulation of simple SUGRA is appropriate for our purposes as the
supermembrane action contains the so-called Wess-Zumino term given by the
integral over a three form potential in superspace, C3. We describe this
formulation in the frame of Wess--Zumino superfield approach, showing how the
basic variations of minimal SUGRA are restricted by the conditions of the
existence of a three-form potential C3 in its superspace. In this language the
effect of dynamical generation of cosmological constant, known to be
characteristic for this formulation of SUGRA, appears in its superfield form,
first described by Ogievetsky and Sokatchev in their formulation of SUGRA as a
theory of axial vector superfield. Secondly, we vary the supermembrane action
with respect to the special minimal SUGRA superfields (basic variations) and
obtain the supercurrent superfields as well as the supergravity superfield
equations with the supermembrane contributions.Comment: 18 pages, no figures. V2: Important references added. The abstract
and presentation have been changed to reflect the overloop with that.
Submitted to the QTS7 Proceedings. J. Phys. style use
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