  We study effects of the internal coherent (Rabi) coupling in vortex lattices
in two-component BECs under rotation. We find how the vortex lattices without
the Rabi coupling known before are connected to the Abrikosov lattice of
integer vortices with increasing the Rabi coupling. We find that 1) for small
Rabi couplings, fractional vortices in triangular or square lattice for small
or large inter-component coupling constitute hexamers or tetramers, namely
multi-dimer bound states made of six or four vortices, respectively, 2) these
bound states are broken into a set of dimers at intermediate Rabi couplings,
and 3) vortices change their partners in various ways depending on the
inter-component coupling to organize themselves for constituting the Abrikosov
lattice of integer vortices at strong Rabi couplings.
