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 theta between the B field and crystal c axis. For anisotropic mass ratio M(c)/M(ab) larger than (3 + square-root 8) and for a range of angles theta(c1) < theta < theta(c2), 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.