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Solids
Penetration of the magnetic field into a 3D ordered Josephson medium at very small values of the pinning parameter
M. A. Zelikman St. Petersburg Polytechnic University
Abstract:
The Meissner state of a 3D Josephson medium is analyzed for stability against small fluctuations of phase discontinuities at contacts. For any form of fluctuations, there exists value
$I_0$ of pinning parameter
$I$ such that the Meissner configuration remains stable if
$I<I_0$. Reasons why the configuration remains stable at small I are considered. Instability arises when the quadratic form of the second variation of Gibbs potential
$G$ is not a positively definite quantity. At small
$I$, the contribution of the Josephson energy to
$G$ is small. The second variation of the magnetic energy, the other component of
$G$, is always a positively definite quadratic form. Therefore, instability may arise only if
$I$ has a finite value. This statement holds true not only for the Meissner but also for any equilibrium configuration. At
$I<I_0$, stability persists up to the boundary of the Meissner state. Then, a sequence of plane vortices parallel to the boundary appears throughout the sample. Thus, vortices appearing at
$I<I_0$ are plane vortices rather than linear. The configurations of currents and the magnetic field profile inside the sample are calculated for
$I<I_0$. Calculation is based on analyzing the continuous variation of the current configuration toward a decrease in the Gibbs potential.
Received: 31.03.2010
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