STRUCTURAL INSTABILITY OF TILTED FLUX LATTICES

We computed the normal modes of vibration of flux lattices in tilted magnetic fields using a Ewald sum technique we recently developed. Soft normal modes at a finite wave vector are observed. For BSCCO the tilt angle at which the instability sets in (theta(i) = 67.7) and the wave vector of instability are in reasonable agreement with recent experimental results of Bolle et al. (theta(i) = 60). Soft phonons are also observed for YBCO at a comparable tilt angle and smaller wave vector of instability.