Quantum interference effects in two double quantum dots-molecules embedded in an Aharonov-Bohm ring

We study equilibrium and non-equilibrium transport of non-interacting electrons through two quantum dot molecules embedded in an Aharonov-Bohm interferometer, and focus in several quantum interference effects occurring in both regimes. We obtain analytical expressions for the transmission and the density of states, and we calculate numerically the current at zero temperature. We show that the system exhibits Fano resonances, total suppression of transmission, and bound states in the continuum. In equilibrium we find a magnetic flux-dependent effective level attraction and lines of perfect transmission when the intramolecular coupling is weak. This feature has strong consequences in the non-equilibrium regime, where the I-V characteristics displays a region of negative differential conductance induced by the magnetic flux. The current suffers an abrupt rise for small bias voltages as consequence of an effective level attraction of the hybridized levels produced by the flux. The decrease of current is result of the destruction of this effect when the bias is increased.