The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Robert F Penna - One of the best experts on this subject based on the ideXlab platform.
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black hole Meissner Effect and entanglement
Physical Review D, 2014Co-Authors: Robert F PennaAbstract:Extremal black holes tend to expel magnetic and electric fields. Fields are unable to reach the horizon because the length of the black hole throat blows up in the extremal limit. The length of the throat is related to the amount of entanglement between modes on either side of the horizon. So it is natural to try to relate the black hole Meissner Effect to entanglement. We derive the black hole Meissner Effect directly from the low temperature limit of two-point functions in the Hartle-Hawking vacuum. Then we discuss several new examples of the black hole Meissner Effect, its applications to astrophysics, and its relationship to gauge invariance.
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black hole Meissner Effect and blandford znajek jets
Physical Review Letters, 2014Co-Authors: Robert F PennaAbstract:Spinning black holes tend to expel magnetic fields. In this way they are similar to superconductors. It has been a persistent concern that this black hole “Meissner Effect” could quench jet power at high spins. This would make it impossible for the rapidly rotating black holes in Cyg X-1 and GRS 1915þ 105 to drive Blandford-Znajek jets. We give a simple geometrical argument why fields which become entirely radial near the horizon are not expelled by the Meissner Effect and may continue to power jets up to the extremal limit. A simple and natural example is a split-monopole field. We stress that ordinary Blandford-Znajek jets are impossible if the Meissner Effect operates and expels the field. Finally, we note that in our general relativistic magnetohydrodynamic simulations of black hole jets, there is no evidence that jets are quenched by the Meissner Effect. The simulated jets develop a large split-monopole component spontaneously which supports our proposal for how the Meissner Effect is evaded and jets from rapidly rotating black holes are powered in nature.
J. E. Hirsch - One of the best experts on this subject based on the ideXlab platform.
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How Alfven’s theorem explains the Meissner Effect
Modern Physics Letters B, 2020Co-Authors: J. E. HirschAbstract:Alfven’s theorem states that in a perfectly conducting fluid magnetic field lines move with the fluid without dissipation. When a metal becomes superconducting in the presence of a magnetic field, magnetic field lines move from the interior to the surface (Meissner Effect) in a reversible way. This indicates that a perfectly conducting fluid is flowing outward. I point this out and show that this fluid carries neither charge nor mass, but carries Effective mass. This implies that the Effective mass of carriers is lowered when a system goes from the normal to the superconducting state, which agrees with the prediction of the unconventional theory of hole superconductivity and with optical experiments in some superconducting materials. The 60-year old conventional understanding of the Meissner Effect ignores Alfven’s theorem and for that reason I argue that it does not provide a valid understanding of real superconductors.
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how alfven s theorem explains the Meissner Effect
arXiv: Superconductivity, 2019Co-Authors: J. E. HirschAbstract:Alfven's theorem states that in a perfectly conducting fluid magnetic field lines move with the fluid without dissipation. When a metal becomes superconducting in the presence of a magnetic field, magnetic field lines move from the interior to the surface (Meissner Effect) in a reversible way. This indicates that a perfectly conducting fluid is flowing outward. We point this out and show that this fluid carries neither charge nor mass, but carries $Effective$ $mass$. This implies that the Effective mass of carriers is lowered when a system goes from the normal to the superconducting state, which agrees with the prediction of the unconventional theory of hole superconductivity and with optical experiments in some superconducting materials. The 60-year old conventional understanding of the Meissner Effect ignores Alfven's theorem and for that reason we argue that it does not provide a valid understanding of real superconductors.
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on the dynamics of the Meissner Effect
Physica Scripta, 2016Co-Authors: J. E. HirschAbstract:The question of how a metal becoming superconducting expels a magnetic field is addressed. It is argued that the conventional theory of superconductivity has not answered this question despite its obvious importance. We argue that the growth of the superconducting region into the normal region and associated expulsion of magnetic field from the superconducting region can only be understood if it is accompanied by motion of charge from the superconducting region into the normal region. From a microscopic point of view it is shown that the perfect diamagnetism of superconductors requires that superconducting electrons reside in orbits of spatial extent , with the London penetration depth. Associated with this physics, the spin–orbit interaction of the electron magnetic moment and the positively charged ionic background gives rise to a 'Spin Meissner' Effect, the generation of a macroscopic spin current near the surface of superconductors. We point out that both the Meissner and the Spin Meissner Effect can be understood dynamically under the assumption that the superfluid condensate wavefunction does not screen itself, just like the for an electron in a hydrogen atom. We argue that the conventional theory of superconductivity cannot explain the Meissner Effect because it does not contain the physical elements discussed here.
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kinetic energy driven superfluidity and superconductivity and the origin of the Meissner Effect
Physica C-superconductivity and Its Applications, 2013Co-Authors: J. E. HirschAbstract:Abstract Superfluidity and superconductivity have many elements in common. However, I argue that their most important commonality has been overlooked: that both are kinetic energy driven. Clear evidence that superfluidity in 4 He is kinetic energy driven is the shape of the λ transition and the negative thermal expansion coefficient below T λ . Clear evidence that superconductivity is kinetic energy driven is the Meissner Effect: I argue that otherwise the Meissner Effect would not take place. Associated with this physics I predict that superconductors expel negative charge from the interior to the surface and that a spin current exists in the ground state of superconductors (spin Meissner Effect). I propose that this common physics of superconductors and superfluids originates in rotational zero point motion. This view of superconductivity and superfluidity implies that rotational zero-point motion is a fundamental property of the quantum world that is missed in the current understanding.
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the origin of the Meissner Effect in new and old superconductors
Physica Scripta, 2012Co-Authors: J. E. HirschAbstract:It is generally believed that superconducting materials are divided into two classes: ?conventional? and ?unconventional?. Conventional superconductors (the elements and thousands of compounds including MgB2) are described by conventional London?BCS?Eliashberg electron?phonon theory. There is no general agreement as to what mechanism or mechanisms describe ?unconventional? superconductors such as the heavy fermions, organics, cuprate and pnictide families. However all superconductors, whether ?conventional? or ?unconventional?, exhibit the Meissner Effect. I argue that there is a single mechanism of superconductivity for all materials, that explains the Meissner Effect and differs from the conventional mechanism in several fundamental aspects: it says that superconductivity is driven by lowering of kinetic rather than potential energy of the charge carriers, it requires conduction by holes rather than electrons in the normal state, and it predicts a non-homogeneous rigid charge distribution and an electric field in the interior of superconductors, and a spin current near the surface. Furthermore I argue that neither the conventional mechanism nor any of the other proposed unconventional mechanisms can explain the Meissner Effect. Superconductivity in materials is discussed in the light of these concepts, some experimental predictions, connections to Dirac's theory, and connections to the superfluidity of 4He.
J Fortagh - One of the best experts on this subject based on the ideXlab platform.
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Meissner Effect in superconducting microtraps
Physical Review Letters, 2008Co-Authors: D Cano, B Kasch, H Hattermann, R Kleiner, C Zimmermann, D Koelle, J FortaghAbstract:We report on the realization and characterization of a magnetic microtrap for ultracold atoms near a straight superconducting Nb wire with circular cross section. The trapped atoms are used to probe the magnetic field outside the superconducting wire. The Meissner Effect shortens the distance between the trap and the wire, reduces the radial magnetic-field gradients, and lowers the trap depth. Measurements of the trap position reveal a complete exclusion of the magnetic field from the superconducting wire for temperatures lower than 6 K. As the temperature is further increased, the magnetic field partially penetrates the superconducting wire; hence the microtrap position is shifted towards the position expected for a normal-conducting wire.
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impact of the Meissner Effect on magnetic microtraps for neutral atoms near superconducting thin films
Physical Review A, 2008Co-Authors: D Cano, B Kasch, H Hattermann, R Kleiner, C Zimmermann, D Koelle, J FortaghAbstract:We theoretically evaluate changes in the magnetic potential arising from the magnetic field near superconducting thin films. An example of an atom chip based on a three-wire configuration has been simulated in the superconducting and the normal conducting state. Inhomogeneous current densities within the superconducting wires were calculated using an energy-minimization routine based on the London theory. The Meissner Effect causes changes to both trap position and oscillation frequencies at short distances from the superconducting surface. Superconducting wires produce much shallower microtraps than normal conducting wires. The results presented in this paper demonstrate the importance of taking the Meissner Effect into account when designing and carrying out experiments on magnetically trapped neutral atoms near superconducting surfaces.
P Wolfle - One of the best experts on this subject based on the ideXlab platform.
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is the nonlinear Meissner Effect unobservable
Physical Review Letters, 1998Co-Authors: M R Li, P J Hirschfeld, P WolfleAbstract:We examine the Effects of nonlocal electrodynamics for a d-wave superconductor on the field dependence of the magnetic penetration depth. The linear field dependence predicted in the local limit, commonly known as the nonlinear Meissner Effect, is instead found to be quadratic, $\delta\lambda\sim H^2$ for fields below a crossover scale $H^*$. This crossover is shown to be geometry dependent and for most orientations of the screening currents is of the same order as or greater than $H_{c1}$, implying that the nonlinear Meissner Effect can not be observed. For special orientations where the current flows along the nodal directions, however, the nonlinear Meissner Effect may be recovered.
G Koren - One of the best experts on this subject based on the ideXlab platform.
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observation of the nonlinear Meissner Effect in ybco thin films evidence for a d wave order parameter in the bulk of the cuprate superconductors
Physical Review Letters, 2004Co-Authors: D E Oates, S H Park, G KorenAbstract:: We present experimental evidence for the observation of the nonlinear Meissner Effect in high-quality epitaxial yttrium barium copper oxide thin films by measuring their intermodulation distortion at microwave frequencies versus temperature. Most of the films measured show a characteristic increase in nonlinearity at low temperatures as predicted by the nonlinear Meissner Effect. We could measure the nonlinear Meissner Effect because intermodulation distortion measurements are an extremely sensitive method that can detect changes in the penetration depth of the order of 1 part in 10(5).