Subharmonic bifurcations of standing wave lattices in a driven ferrofluid system

Superlattice standing waves arising on the surface of ferrofluids that are driven by an ac magnetic field are investigated experimentally. Several different types are obtained through successive spatial period doublings, which are mediated by resonant mode interactions. The observed superlattices are quite diverse, depending on the relevant base Fourier modes, the orientation and the number of emerged subharmonic modes, and the phase difference among the involved modes all together. On the other hand, their temporal evolutions are all either period-1 (harmonic) or period-2 (subharmonic).