INCLINED-FIELD STRUCTURE, MORPHOLOGY, AND PINNING OF THE VORTEX LATTICE IN MICROTWINNED YBA2CU3O7

A detailed small-angle neutron scattering study of the vortex lattice in a single crystal of YBa2Cu3O7 was made for a field of 0.5 tesla inc lined at angles between 0 and 80 degrees to the crystalline c axis. Th e vortex lattice is triangular for all angles, and for angles less tha n or equal to 70 degrees its orientation adjusts itself to maximize th e pinning energy to densely and highly regularly spaced twin planes. T hese observations have important implications for the microscopic flux -pinning mechanism, and hence for the critical current achievable in Y BaCu3O7. For large angles (about 80 degrees) the vortex lattice consis ts of independent chains in the orientation predicted by anisotropic L ondon theory.