We consider the formation of bright solitons in a mixture of Bose and Fermi
degenerate gases confined in a three-dimensional elongated harmonic trap. The
Bose and Fermi atoms are assumed to effectively attract each other whereas
bosonic atoms repel each other. Strong enough attraction between bosonic and
fermionic components can change the character of the interaction within the
bosonic cloud from repulsive to attractive making thus possible the generation
of bright solitons in the mixture. On the other hand, such structures might be
in danger due to the collapse phenomenon existing in attractive gases. We show,
however, that under some conditions (defined by the strength of the Bose-Fermi
components attraction) the structures which neither spread nor collapse can be
generated. For elongated enough traps the formation of solitons is possible
even at the ``natural'' value of the mutual Bose-Fermi (87Rb -40K in
our case) scattering length.Comment: 6 pages, 6 figures, 1 tabl