21,221 research outputs found
Superconductivity-Induced Anderson Localisation
We have studied the effect of a random superconducting order parameter on the
localization of quasi-particles, by numerical finite size scaling of the
Bogoliubov-de Gennes tight-binding Hamiltonian. Anderson localization is
obtained in d=2 and a mobility edge where the states localize is observed in
d=3. The critical behavior and localization exponent are universal within error
bars both for real and complex random order parameter. Experimentally these
results imply a suppression of the electronic contribution to thermal transport
from states above the bulk energy gap.Comment: 4 pages, revtex file, 3 postscript figure
Freund-Rubin Revisited
We utilise the duality between M theory and Type IIA string theory to show
the existence of Freund-Rubin compactifications of M theory on 7-manifolds with
singularities supporting chiral fermions. This leads to a concrete way to study
phenomenologically interesting quantum gravity vacua using a holographically
dual three dimensional field theory.Comment: reference adde
The Threebrane Soliton of the M-Fivebrane
We discuss the supersymmetry algebra of the M theory fivebrane and obtain a
new threebrane soliton preserving half of the six-dimensional supersymmetry.
This solution is dimensionally reduced to various D-p-branes.Comment: 10 pages, phyzz
A New Massive Type IIA Supergravity From Compactification
We consider the most general form for eleven dimensional supersymmetry
compatible with on-shell superfields. This allows for the introduction of a
conformal Spin(1,10) connection. In eleven dimensional Minkowski space this
modification is trivial and can be removed by a field redefinition, however,
upon compactification on S^1 it is possible to introduce a non-trivial `Wilson
line'. The resulting ten dimensional supergravity has massive 1-form and 3-form
potentials and a cosmological constant. This theory does not possess a
supersymmetric eightbrane soliton but it does admit a supersymmetric non-static
cosmological solution.Comment: 13 pages, phyzzx. The introduction is clarifed and a reference adde
Oscillating chiral currents in nanotubes: a route to nanoscale magnetic test tubes
With a view to optimising the design of carbon-nanotube (CNT) windmills and
to maximising the internal magnetic field generated by chiral currents, we
present analytical results for the group velocity components of an electron
flux through chiral carbon nanotubes. Chiral currents are shown to exhibit a
rich behaviour and can even change sign and oscillate as the energy of the
electrons is increased. We find that the transverse velocity and associated
angular momentum of electrons is a maximum for non-metallic CNTs with a chiral
angle of 18. Such CNTs are therefore the optimal choice for CNT windmills
and also generate the largest internal magnetic field for a given longitudinal
current. For a longitudinal current of order amps, this field can be
of order Teslas, which is sufficient to produce interesting spintronic
effects and a significant contribution to the self inductance.Comment: 4 pages, 1 figur
Suppression of Giant Magnetoresistance by a superconducting contact
We predict that current perpendicular to the plane (CPP) giant
magnetoresistance (GMR) in a phase-coherent magnetic multilayer is suppressed
when one of the contacts is superconducting. This is a consequence of a
superconductivity-induced magneto-resistive (SMR) effect, whereby the
conductance of the ferromagnetically aligned state is drastically reduced by
superconductivity. To demonstrate this effect, we compute the GMR ratio of
clean (Cu/Co)_nCu and (Cu/Co)_nPb multilayers, described by an ab-initio spd
tight binding Hamiltonian. By analyzing a simpler model with two orbitals per
site, we also show that the suppression survives in the presence of elastic
scattering by impurities.Comment: 5 pages, 4 figures. Submitted to PR
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