We derive the wave-vector-dependent elastic moduli for a flux line lattice in compounds with underlying tetragonal crystalline symmetry. We find that it is essential to retain wave-vector dependence of the moduli when dealing with compounds where κ is large, as it is in the high-$T_c$ materials. We use our results to establish a Lindemann criterion for flux lattice melting, which we then compare with experimental data on two materials, and find excellent agreement. The melting curves are suppressed well below the mean-field superconducting-normal transition line and are linear in temperature over a wide range of magnetic fields. The point H=0, T=$T_c$ is approached as 1-T/$T_c$∼$H^{1/2}$. The degree of suppression of the melting curves among the different compounds is accounted for in the main by differences in mass anisotropy.

• Received 4 May 1989

DOI:https://doi.org/10.1103/PhysRevB.40.6763