9,605 research outputs found

### Electrodynamics of superconductors

An alternate set of equations to describe the electrodynamics of
superconductors at a macroscopic level is proposed. These equations resemble
equations originally proposed by the London brothers but later discarded by
them. Unlike the conventional London equations the alternate equations are
relativistically covariant, and they can be understood as arising from the
'rigidity' of the superfluid wave function in a relativistically covariant
microscopic theory. They predict that an internal 'spontaneous' electric field
exists in superconductors, and that externally applied electric fields, both
longitudinal and transverse, are screened over a London penetration length, as
magnetic fields are. The associated longitudinal dielectric function predicts a
much steeper plasmon dispersion relation than the conventional theory, and a
blue shift of the minimum plasmon frequency for small samples. It is argued
that the conventional London equations lead to difficulties that are removed in
the present theory, and that the proposed equations do not contradict any known
experimental facts. Experimental tests are discussed.Comment: Small changes following referee's and editor's comments; to be
published in Phys.Rev.

### Modified Josephson Relation

For type II superconductors, Josephson has shown that vortices moving with
velocity v_L create an effective electric field E'=-v_L x B. By definition the
effective electric field is gradient of the electrochemical potential, what is
the quantity corresponding to voltage observed with the use of Ohmic contacts.
It relates to the true electric field E via the local chemical potential mu as
E'=E - grad(mu)/e. We argue that at low temperatures the true electric field in
the bulk can be approximated by a modified Josephson relation E=(v_s-v_L) x B,
where v_S is the condensate velocity.Comment: 3 page

### Probing New Physics via an Angular Analysis of B --> V1 V2 decays

We show that an angular analysis of B --> V1 V2 decays yields numerous tests
for new physics in the decay amplitudes. Unlike direct CP asymmetries, many of
these new-physics observables are nonzero even if the strong phase differences
vanish. For certain observables, neither time-dependent measurements nor
tagging is necessary. Should a signal for new physics be found, one can place a
lower limit on the size of the new-physics parameters, as well as on their
effect on the measurement of the phase of B0--Bbar0 mixing.Comment: 9 pages, plain latex, no figures. Title modified slightly. Paragraph
added about viability of method. Conclusions unchanged. To be published in
Europhysics Letter

### Gravitoelectromagnetism and Dark Energy in Superconductors

A gravitomagnetic analogue of the London moment in superconductors can
explain the anomalous Cooper pair mass excess reported by Janet Tate.
Ultimately the gravitomagnetic London moment is attributed to the breaking of
the principle of general covariance in superconductors. This naturally implies
non-conservation of classical energy-momentum. Possible relation with the
manifestation of dark energy in superconductors is questioned.Comment: 10 pages. Poster presented at "From Quantum to Cosmos - Fundamental
Physics Research in Space" 22-24 May 2006, To Appear in Int. J. Mod. Phys.

### Spin currents in superconductors

It is argued that experiments on rotating superconductors provide evidence
for the existence of macroscopic spin currents in superconductors in the
absence of applied external fields. Furthermore it is shown that the model of
hole superconductivity predicts the existence of such currents in all
superconductors. In addition it is pointed out that spin currents are required
within a related macroscopic (London-like) electrodynamic description of
superconductors recently proposed. The spin current arises through an intrinsic
spin Hall effect when negative charge is expelled from the interior of the
metal upon the transition to the superconducting state

### Vortex Penetration into a Type II Superconductor due to a Mesoscopic External Current

Applying the London theory we study curved vortices produced by an external
current near and parallel to the surface of a type II superconductor. By
minimizing the energy functional we find the contour describing the hard core
of the flux line, and predict the threshold current for entrance of the first
vortex. We assume that the vortex entrance is allowed due to surface defects,
despite the Bean-Livingston barrier. Compared to the usual situation with a
homogeneous magnetic field, the main effect of the present geometry is that
larger magnetic fields can be applied locally before vortices enter the
superconducting sample. It is argued that this effect can be further enhanced
in anisotropic superconductors.Comment: 9 pages, 14 figure

### Can one detect new physics in I=0 and/or I=2 contributions to the decays B --> pi pi?

We study the effects of new-physics contributions to B --> pi pi decays,
which can be parametrized as four new complex quantities. A simple analysis is
provided by utilizing the reparametrization invariance of the decay amplitudes.
We find that six quantities can be reabsorbed into the definitions of Standard
Model-like parameters. As a result, the usual isospin analysis provides only
two constraints on new physics which are independent of estimates for the
Standard Model contributions. In particular, we show that one is not sensitive
to new physics affecting the I=0 amplitudes. On the other hand, I=2 new physics
can be detected, and its parameters can be measured by using independent
determinations of the weak phases. We obtain constraints on these new-physics
parameters through a fit to the current experimental data.Comment: 8 pages, RevTe

### Measuring Strong and Weak Phases in Time-Independent B Decays

Flavor SU(3) symmetry implies certain relations among $B$-decay amplitudes to
$\pi\pi$, $\pi K$ and $K {\bar K}$ final states, when annihilation-like
diagrams are neglected. Using three triangle relations, we show how to measure
the weak CKM phases $\alpha$ and $\gamma$ using time-independent rate
measurements only. In addition, one obtains all the strong final-state phases
and the magnitudes of individual terms describing tree (spectator),
color-suppressed and penguin diagrams. Many independent measurements of these
quantities can be made with this method, which helps to eliminate possible
discrete ambiguities and to estimate the size of SU(3)-breaking effects.Comment: 2 figures available from the authors upon request, 12
pages,UdeM-LPN-TH-94-19

### Effects of disorder on the vortex charge

We study the influence of disorder on the vortex charge, both due to random
pinning of the vortices and due to scattering off non-magnetic impurities. In
the case when there are no impurities present, but the vortices are randomly
distributed, the effect is very small, except when two or more vortices are
close by. When impurities are present, they have a noticeable effect on the
vortex charge. This, together with the effect of temperature, changes
appreciably the vortex charge. In the case of an attractive impurity potential
the sign of the charge naturally changes.Comment: 10 pages, 16 figures. Accepted in Phys. Rev.

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