Tilt-wave instability of the flux-line lattice in anisotropic superconductors

The stability of the Abrikosov flux-line lattice for uniaxially anisotropic superconductors has been studied in the London approximation as a function of the anisotropic mass ratio and the angle θ between the B field and crystal c axis. For anisotropic mass ratio ${\mathit{M}}_{\mathit{c}}$/${\mathit{M}}_{\mathit{a}\mathit{b}}$ larger than (3+ √8 ) and for a range of angles ${\mathrm{\theta }}_{\mathit{c}1}$${\mathrm{\theta }}_{\mathit{c}2}$, the straight flux lines become unstable and a tilt-wave instability occurs, irrespective of the magnitude of the B field. We show that this instability occurs for a variety of cutoff schemes (which are needed to make London theory finite). The instability is probably related to the formation of a ‘‘combined’’ lattice of flux lines in which two species of vortices coexist simultaneously but run in different directions.