  We analyze the energetic and dynamical properties of bright-bright (BB)
soliton pairs in a binary mixture of Bose-Einstein condensates subjected to the
action of a combined optical lattice, acting as an external potential for the
first species, while modulating the intraspecies coupling constant of the
second. In particular, we use a variational approach and direct numerical
integrations to investigate the existence and stability of BB solitons in which
the two species are either spatially separated (split soliton) or located at
the same optical lattice site (overlapped soliton). The dependence of these
solitons on the interspecies interaction parameter is explicitly investigated.
For repulsive interspecies interaction we show the existence of a series of
critical values at which transitions from an initially overlapped soliton to
split solitons occur. For attractive interspecies interaction only single
direct transitions from split to overlapped BB solitons are found. The
possibility to use split solitons for indirect measurements of scattering
lengths is also suggested.
