Large range of validity of linear elasticity of the vortex lattice in high-Tcsuperconductors

Linear elasticity theory of the vortex lattice in anisotropic and layered superconductors has a much wider range of applicability than in isotropic superconductors. This finding is used to calculate the energy barrier for thermally activated depinning of vortices from columnar pins along the c axis. The activation energy of these most effective line pins is strongly reduced by anisotropy. For very large anisotropy as in ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$, the length of the depinning vortex segment formally becomes shorter than the layer spacing; this means that the pancake vortices in the CuO layers depin individually.