Elastic properties of flux lattices in anisotropic high-Tcsuperconductors

The elastic moduli of the two-dimensional flux-line lattice in a uniaxial superconductor are evaluated for an arbitrary orientation of vortices (i.e., of the magnetic induction) within the crystal in intermediate fields. For the flux lines in the basal a-b plane the ratio of the simple shear moduli, corresponding to displacements normal and parallel to the basal plane, is shown to equal (${\mathrm{m}}_3$/${\mathrm{m}}_1$ ${)}^2$ where ${\mathrm{m}}_3$ and ${\mathrm{m}}_1$ are the masses along the c axis and the basal plane, respectively. For ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ this amounts to a factor exceeding 600. The uniaxial crystal symmetry defines a preferred orientation to the flux lattice and doubles the number of independent elastic constants.