  We evaluate the particle current flowing in steady state through a
Bose-Einstein condensate subject to a constant force in a quasi-onedimensional
lattice and to attractive interactions from fermionic atoms that are localized
in various configurations inside the lattice wells. The system is treated
within a Bose-Hubbard tight binding model by an out-of-equilibrium Green's
function approach. A new band gap opens up when the lattice period is doubled
by locating the fermions in alternate wells and yields an interference pattern
in the transmittivity on varying the intensity of the driving force. The
positions of the transmittivity minima are determined by matching the period of
Bloch oscillations and the time for tunnelling across the band gap. Massive
disorder in the distribution of the fermions will wash out the interference
pattern, but the same period doubling of the lattice can be experimentally
realized in a four-beam set-up. We report illustrative numerical results for a
mixture of 87Rb and 40K atoms in an optical lattice created by laser beams with
a wavelength of 763 nm.
