  In a rotating two-component Bose-Einstein condensate (BEC), the traditional
triangular vortex lattice can be replaced by a rectangular vortex lattice or
even a structure characterized in terms of vortex sheets, depending on the
interspecies interactions. We study the dynamics of this system by analyzing
the Bogoliubov excitation spectrum. Excitations familiar to BEC vortex systems
are found such as Tkachenko modes, hydrodynamic modes and surface waves,
however, the complex two-component morphology also gives rise to new phenomena
including shear flow between vortex sheets.
