It is shown that in a nonellipsoidal sample of type-I superconductor, for values of the applied magnetic field exceeding a thermodynamic transition field which is defined, the magnetization process is completely governed by a metastable mechanism which is analyzed. The same mechanism is responsible for the frequently observed irreversible behavior.

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A detailed electromagnetic and thermodynamical theory of the intermediate state in type-1 superconductors is worked out in the I,andau laminar geometry. It is shown that the Landau s domain bounded by a convex wall where the magnetic field very nearly approaches the critical value is likely to be near the most stable configuration.The analysis of the field distribution in the n laminas provides a qualitative explanation of the experimentally observed small importance of the branching that Landau first suggested. Explicit analytical expressions of the various contributions to the free energy are derived as functions of the applied magnetic field and of the superconductive fraction. This allows the exact formulation of the equations yielding the transition fields at the ends of the intermediate range. At the lowest order, the departure of the field from the ideal value varies predominantly as {4/l)'~~at the diamagnetic intermediate-phase transition and as (&/l) at the intermediate normal-phase transition, 4 being the surface energy and l the thickness of the sample.

A. FORTINIThe self-consistent linearized Poisson equation leading to the screened potential of an ionized centre embedded in a free carrier plasma, is rewritten in a closed form taking into account the quantum character of the plasma. Complete resolution in the case of Boltzmann statistics clearly shows how quantum corrections cause a departure of the screening length from its usual semiclassical value. Quantum corrections are also responsible for the anisotropy of the screening in a static magnetic field. Calculations are worked out for the case of a strong quantizing field.Die selbstkonsistente linearisierte Poissongleichung, die zu dem abgeschirmten Potential eines ionisierten Zentrums, das in einem Plasma freier Trager eingebettet ist, fiihrt, wird in einer geschlossenen Form umformuliert unter Berucksichtigung des Quantencharakters des Plasmas. Eine vollstandige Losung fur den Fall der Boltzmannstatistik zeigt deutlich, wie die Quantenkorrekturen eine Abweichung der Abschirmlange von ihrem normalen halbklassischen Wert verursachen. Die Quantenkorrekturen sind auch verantwortlich fur die Anisotropie der Abschirmung im statischen Magnetfeld. Berechnungen werden fur den Fall eines starken quantisierenden Feldes durchgefiihrt.

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