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2015

Annals of Physics

The analisis of Pippard [1] for the growth of the normal phase into the superconducting phase in the presence of a magnetic field H > Hc is applied in reverse to the case H < Hc (Hc =critical magnetic field). We carry out the analysis both for a planar and a cylindrical geometry. As the superconducting phase grows into the normal phase, a supercurrent is generated at the superconductornormal phase boundary that flows in direction opposite to the Faraday electric field resulting from the moving phase boundary. This supercurrent motion is in direction opposite to what is dictated by the Lorentz force on the current carriers, and in addition requires that mechanical momentum of opposite sign be tranferred to the system as a whole to ensure momentum conservation. In the cylindrical geometry case, a macroscopic torque of unknown origin acts on the body as a whole as the magnetic field is expelled. We argue that the conventional BCS-London theory of superconductivity cannot explain these facts, and that as a consequence the Meissner effect remains unexplained within the conventional theory of superconductivity. We propose that the Meissner effect can only be understood by assuming that there is motion of charge in direction perpendicular to the normal-superconductor phase boundary and point out that the unconventional theory of hole superconductivity describes this physics. PACS numbers:Here, H = Hẑ, J = J yŷ , E = E yŷ . Application of Faraday's law using a contour with one edge at the phase

Section: Angular Momentummentioning

confidence: 99%

Dynamics of the normal–superconductor phase transition and the puzzle of the Meissner effect

2015

Annals of Physics

“…The corresponding experiment for the case where the magnetic field is expelled from the superconductor has not been performed, nor has the question been considered theoretically (except for ref. [6]).…”

Section: Angular Momentum In the Meissner Currentmentioning

confidence: 99%

“…This electric field pushes the positive ions in the same direction as the electrons in the Meissner current, i.e. to acquire mechanical angular momentum parallel to the electronic angular momentum in the Meissner current [6], so it is clear that this effect has the wrong sign to resolve the angular momentum question.…”

Section: Meissner Effect In the Conventional Frameworkmentioning

confidence: 99%

“…Consider a metal at zero temperature in an external magnetic field that is lowered from right above to right below the critical field. The electrons can extract angular momentum from the electromagnetic field only if there is a radial flow of charge [6] (see next section). However no radial charge flow is predicted in the conventional theory.…”

Section: Meissner Effect In the Conventional Frameworkmentioning

confidence: 99%

“…However: neither BCS theory nor London theory address the question of how the system attains the final (superconducting) state where the magnetic field is excluded starting from an initial (normal) state where magnetic field exists in the interior [6]. Specifically: (i) What is the nature of the f orce that causes the superfluid electrons near the surface to all acquire a velocity in the direction required to screen the external magnetic field?…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The missing angular momentum of superconductors

J. Phys.: Condens. Matter

2008

We point out that the Meissner effect, the process by which a superconductor expels magnetic field from its interior, represents an unsolved puzzle within the London-Bardeen-Cooper-Schrieffer theoretical framework used to describe the physics of conventional superconductors, because it appears to give rise to non-conservation of angular momentum. Possible ways to avoid this inconsistency within the conventional theory of superconductivity are argued to be far-fetched. Consequently, we argue that unless/until a consistent explanation is put forth, the existence of the Meissner effect represents an anomaly that casts doubt on the validity of the conventional framework. Instead, we point out that three elements of the unconventional theory of hole superconductivity (that are not part of the conventional theory) allow for a consistent explanation of the Meissner effect, namely: (i) that the charge distribution in superconductors is macroscopically inhomogeneous, (ii) that superconducting electrons reside in mesoscopic orbits of radius 2λ(L) (λ(L) = London penetration depth), and (iii) that spin-orbit coupling plays an essential role in superconductivity.

Spin Meissner effect in superconductors and the origin of the Meissner effect

2008

Europhys. Lett.

189

We propose a dynamical explanation of the Meissner effect in superconductors and predict the existence of a spin Meissner effect: that a macroscopic spin current flows within a London penetration depth λL of the surface of superconductors in the absence of applied external fields, with carrier density = the superfluid density and carrier speed v = /(4meλL) (me =bare electron mass). The two members of a Cooper pair circulate in orbits of radius 2λL in opposite direction and the spin current in a Cooper pair has orbital angular momentum . Our description also provides a 'geometric' interpretation of the difference between type I and type II superconductors.PACS numbers: