11,308 research outputs found
Fermi-liquid effects in the gapless state of marginally thin superconducting films
We present low temperature tunneling density-of-states measurements in Al
films in high parallel magnetic fields. The thickness range of the films, t=6-9
nm, was chosen so that the orbital and Zeeman contributions to their parallel
critical fields were comparable. In this quasi-spin paramagnetically limited
configuration, the field produces a significant suppression of the gap, and at
high fields the gapless state is reached. By comparing measured and calculated
tunneling spectra we are able to extract the value of the antisymmetric
Fermi-liquid parameter G^0 and thereby deduce the quasiparticle density
dependence of the effective parameter G^0_{eff} across the gapless state.Comment: 6 pages, 4 figure
Consistency of a Causal Theory of Radiative Reaction with the Optical Theorem
The Abraham-Lorentz-Dirac equation for a point electron, while suffering from
runaway solutions and an acausal response to external forces, is compatible
with the optical theorem. We show that a theory of radiative reaction that
allows for a finite charge distribution is not only causal and free of runaway
solutions, but is also consistent with the optical theorem and the standard
formula for the Rayleigh scattering cross section.Comment: 4 pages, 2 figure
Fermionic Bound States and Pseudoscalar Exchange
We discuss the possibility that fermions bind due to Higgs or pseudoscalar
exchange. It is reasonable to believe on qualitative grounds that this can
occur for fermions with a mass larger than 800-900 GeV. An exchange of a
pseudoscalar boson leads in the non-relativistic limit to an unacceptable
potential which behaves like 1/r^3 at the origin. We show that this singular
behaviour is smeared out when relativistic effects are included
Magneto-controlled nonlinear optical materials
We exploit theoretically a magneto-controlled nonlinear optical material
which contains ferromagnetic nanoparticles with a non-magnetic metallic
nonlinear shell in a host fluid. Such an optical material can have anisotropic
linear and nonlinear optical properties and a giant enhancement of
nonlinearity, as well as an attractive figure of merit.Comment: 11 pages, 2 figures. To be published in Appl. Phys. Let
Macroscopic Aharonov--Bohm Effect in Type-I Superconductors
In type-I superconducting cylinders bulk superconductivity is destroyed above
the first critical current. Below the second critical current the `type-I mixed
state' displays fluctuation superconductivity which contributes to the total
current. A magnetic flux on the axis of the cylinder can change the second
critical current by as much as 50 percent so that half a flux quantum can
switch the cylinder from normal conduction to superconductivity: the
Aharonov--Bohm effect manifests itself in macroscopically large resistance
changes of the cylinder.Comment: five pages, one figur
Temperature-dependent resistivity of suspended graphene
In this paper we investigate the electron-phonon contribution to the
resistivity of suspended single layer graphene. In-plane as well as flexural
phonons are addressed in different temperature regimes. We focus on the
intrinsic electron-phonon coupling due to the interaction of electrons with
elastic deformations in the graphene membrane. The competition between screened
deformation potential vs fictitious gauge field coupling is discussed, together
with the role of tension in the suspended flake. In the absence of tension,
flexural phonons dominate the phonon contribution to the resistivity at any
temperature with a and dependence at low and high
temperatures, respectively. Sample-specific tension suppresses the contribution
due to flexural phonons, yielding a linear temperature dependence due to
in-plane modes. We compare our results with recent experiments.Comment: 11 pages, 3 figure
Energy-momentum balance in quantum dielectrics
We calculate the energy-momentum balance in quantum dielectrics such as
Bose-Einstein condensates. In agreement with the experiment [G. K. Campbell et
al. Phys. Rev. Lett. 94, 170403 (2005)] variations of the Minkowski momentum
are imprinted onto the phase, whereas the Abraham tensor drives the flow of the
dielectric. Our analysis indicates that the Abraham-Minkowski controversy has
its root in the Roentgen interaction of the electromagnetic field in dielectric
media
The Range of Validity for the Kelvin Force
In a recent Letter, Luo, Du and Huang reported a novel convective instability
driven by a force rarely studied before -- that exerted by an external magnetic
field on a strongly magnetizable liquid. The associated physics is surprisingly
rich and promises many more interesting results for the future. Unfortunately,
the analysis starts from a misconception and employs the Kelvin force outside
its range of validity. Since few would recognize this as a mistake, and since
its consequence in the given experiment is particularly direct and critical,
this is a point well worth being clarified, and clearly understood.Comment: 1 pag
A note on the analogy between superfluids and cosmology
A new analogy between superfluid systems and cosmology is here presented,
which relies strongly on the following ingredient: the back-reaction of the
vacuum to the quanta of sound waves. We show how the presence of thermal
phonons, the excitations above the quantum vacuum for , enable us to
deduce an hydrodynamical equation formally similar to the one obtained for a
perfect fluid in a Universe obeying the Friedmann-Robertson-Walker metric.Comment: Accepted for publication in Modern Physics Letters
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