11,596 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.
Mission Capabilities of Ion Engines. Phase II
Payloads and mission times were calculated for space vehicles propelled by ion rockets using nuclear power supplies having specific weights from 10 t o 50 lb/kw. Included in the study were five missions: low-altitude lunar satellite, low-altitude Venus satellite, solar probe, Saturn probe, and a Jupiter satellite with a circular orbit at the altitude of Jupiter's fourth moon. The variation of payload with the ration of power supply weight to gross weight was studied and the optimum power levels thereby determined. The ion rocket payload capabilities were compared with those of high-thrust vehicles using hydrogen-oxygen rockets and tungsten-core nuclear rockets; in addition the performance of high- and low-thrust systems staged in combination has been investigated. Launch vehicles considered in this study were the Atlas-Centaur, the Saturn C-1, and the Saturn C-5
Reducing Penguin Pollution
The most common decay used for measuring 2beta_s, the phase of Bs-Bsbar
mixing, is Bs -> J/psi phi. This decay is dominated by the colour-suppressed
tree diagram, but there are other contributions due to gluonic and electroweak
penguin diagrams. These are often referred to as "penguin pollution" (PP)
because their inclusion in the amplitude leads to a theoretical error in the
extraction of 2beta_s from the data. In the standard model (SM), it is
estimated that the PP is negligible, but there is some uncertainty as to its
exact size. Now, phi_s^{c\bar{c}s} (the measured value of 2beta_s) is small, in
agreement with the SM, but still has significant experimental errors. When
these are reduced, if one hopes to be able to see clear evidence of new physics
(NP), it is crucial to have the theoretical error under control. In this paper,
we show that, using a modification of the angular analysis currently used to
measure phi_s^{c\bar{c}s} in Bs -> J/psi phi, one can reduce the theoretical
error due to PP. Theoretical input is still required, but it is much more
modest than entirely neglecting the PP. If phi_s^{c\bar{c}s} differs from the
SM prediction, this points to NP in the mixing. There is also enough
information to test for NP in the decay. This method can be applied to all
Bs/Bsbar -> V1 V2 decays.Comment: 17 pages, latex, extensive discussion of theoretical error added,
reference added. Further revision: even more detailed discussion of
theoretical error added, as well as an explanation of why the NP strong phase
is negligibl
Symmetries and collective excitations in large superconducting circuits
The intriguing appeal of circuits lies in their modularity and ease of
fabrication. Based on a toolbox of simple building blocks, circuits present a
powerful framework for achieving new functionality by combining circuit
elements into larger networks. It is an open question to what degree modularity
also holds for quantum circuits -- circuits made of superconducting material,
in which electric voltages and currents are governed by the laws of quantum
physics. If realizable, quantum coherence in larger circuit networks has great
potential for advances in quantum information processing including topological
protection from decoherence. Here, we present theory suitable for quantitative
modeling of such large circuits and discuss its application to the fluxonium
device. Our approach makes use of approximate symmetries exhibited by the
circuit, and enables us to obtain new predictions for the energy spectrum of
the fluxonium device which can be tested with current experimental technology
Correcting 100 years of misunderstanding: electric fields in superconductors, hole superconductivity, and the Meissner effect
From the outset of superconductivity research it was assumed that no
electrostatic fields could exist inside superconductors, and this assumption
was incorporated into conventional London electrodynamics. Yet the London
brothers themselves initially (in 1935) had proposed an electrodynamic theory
of superconductors that allowed for static electric fields in their interior,
which they unfortunately discarded a year later. I argue that the Meissner
effect in superconductors necessitates the existence of an electrostatic field
in their interior, originating in the expulsion of negative charge from the
interior to the surface when a metal becomes superconducting. The theory of
hole superconductivity predicts this physics, and associated with it a
macroscopic spin current in the ground state of superconductors ("Spin Meissner
effect"), qualitatively different from what is predicted by conventional
BCS-London theory. A new London-like electrodynamic description of
superconductors is proposed to describe this physics. Within this theory
superconductivity is driven by lowering of quantum kinetic energy, the fact
that the Coulomb repulsion strongly depends on the character of the charge
carriers, namely whether electron- or hole-like, and the spin-orbit
interaction. The electron-phonon interaction does not play a significant role,
yet the existence of an isotope effect in many superconductors is easily
understood. In the strong coupling regime the theory appears to favor local
charge inhomogeneity. The theory is proposed to apply to all superconducting
materials, from the elements to the high cuprates and pnictides, is
highly falsifiable, and explains a wide variety of experimental observations.Comment: Proceedings of the conference "Quantum phenomena in complex matter
2011 - Stripes 2011", Rome, 10 July -16 July 2011, to be published in J.
Supercond. Nov. Mag
- …