Mode locking and lattice orientations of driven vortex matter in amorphous MoGe films

We have investigated flow properties of a current driven, vortex lattice in amorphous MoGe films by mode locking (ML) experiment. ML is a dynamic resonance between a collective velocity modulation of “lattice mode” and a superimposed ac (rf) current on top of a dc current. Tracing the resonance features against magnetic field, we find two specific orientations of lattice flow with respect to the flow direction in the flux-flow state: one is an orientation characterized by a principal axis of the driven lattice parallel to the flow direction, and the other is another orientation where one of the lattice axes is perpendicular to the flow direction.