Josephson penetration depth: Definition from Answers.com

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In superconductivity, Josephson penetration depth characterizes the typical length on which an externally-applied magnetic field penetrates into the long Josephson junction. Josephson penetration depth is usually denoted as $λ J$ and is given by the following expression (in SI):

$\lambda_J=\sqrt{\frac{\Phi_0}{2\pi\mu_0 d' j_c}},$

where $Φ 0$ is the magnetic flux quantum, $j c$ is the critical current density $(A / cm 2)$ , and $d'$ characterizes the inductance of the superconducting electrodes

$d'=d_I +\lambda_1 \coth\left(\frac{d_1}{\lambda_1}\right) +\lambda_2 \coth\left(\frac{d_2}{\lambda_2}\right),$

where $d I$ is the thickness of the Josephson barrier (usually insulator), $d 1,2$ are the thicknesses of superconducting electrodes, and $λ 1,2$ are their London penetration depths.

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