Abstract
The discovery of the Meissner (Meissner–Ochsenfeld) effect in 1933 was an incontestable turning point in the history of superconductivity. First, it demonstrated that superconductivity is an unknown before equilibrium state of matter, thus allowing to use the power of thermodynamics for its study. This provided a justification for the two-fluid model of Gorter and Casimir, a seminal thermodynamic theory founded on a postulate of zero entropy of the superconducting (S) component of conduction electrons. Second, the Meissner effect demonstrated that, apart from zero electric resistivity, the S phase is also characterized by zero magnetic induction. The latter property is used as a basic postulate in the theory of F. and H. London, which underlies the understanding of electromagnetic properties of superconductors. Here the experimental and theoretical aspects of the Meissner effect are reviewed. The reader will see that, in spite of almost nine decades age, the London theory still contains questions, the answers to which can lead to a revision of the standard picture of the Meissner state (MS) and, if so, of other equilibrium superconducting states. An attempt is made to take a fresh look at electrodynamics of the MS and try to work out with the issues associated with the description of this most important state of all superconductors. It is shown that the concept of Cooper’s pairing along with the Bohr–Sommerfeld quantization condition allows one to construct a semi-classical theoretical model consistently addressing properties of the MS and beyond, including non-equilibrium properties of superconductors caused by the total current. As follows from the model, the three “big zeros” of superconductivity (zero resistance, zero induction and zero entropy) have equal weight and grow from a single root: quantization of the angular momentum of paired electrons. The model predicts some yet unknown effects. If confirmed, they can help in studies of microscopic properties of all superconductors. Preliminary experimental results suggesting the need to revise the standard picture of the MS are presented.
Highlights
The history of the Meissner effect takes its origin from experiments of Keesom and coworkers of 1932 [1], in which it was revealed that the electron heat capacity in tin and thallium experiences a discontinuous jump near the critical temperature of the transition from the normal (N) to the superconducting (S) state Tc, a constant of the material in question
This means that there is no contradiction between results of the first two arrangements with those of the third one, and that Meissner and Ochsenfeld were exactly right in their interpretation
As it was first shown by Kok [21], the cubic temperature dependence of the electron heat capacity leads to the quadratic temperature dependence of the thermodynamic critical field Hc(T ), which is consistent with experimental data
Summary
The history of the Meissner effect takes its origin from experiments of Keesom and coworkers of 1932 [1], in which it was revealed that the electron heat capacity in tin and thallium experiences a discontinuous jump near the critical temperature of the transition from the normal (N) to the superconducting (S) state Tc, a constant of the material in question. On switching off the applied field keeping the sample superconducting, the field inside remained unchanged; at the same time the field outside decreased but it did not become zero In regard of this arrangement, the authors noted that their observations may look inconsistent with the statement about zero permeability. One can add that the observed field enhancement inside the tube sample is consistent with recent direct measurements of the field near the sample in the intermediate state [12] This means that there is no contradiction between results of the first two arrangements with those of the third one, and that Meissner and Ochsenfeld were exactly right in their interpretation. To discuss a possible way to resolve it is the main objective of this review
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