Effects of the electron-electron interaction on electronic transport through the antibonding orbital of a longitudinally embedded double quantum dot

The effects of the on-site electron-electron (e-e) interaction U on the electronic transport across two longitudinally embedded quantum dots in the regime in which the antibonding (AB) state of the isolated composite system is aligned with the Fermi level at the leads are investigated. This regime occurs when the dot orbital energy epsilon(d) is negative and equal in magnitude to the hopping probability between the orbitals on the two dots. In the noninteracting case, the conductance approaches asymptotically the conductance quantum G(0)=2e(2)/h as epsilon(d) decreases; in addition, the contribution of the AB channel to the conductance tends to 1. As shown here, this picture is substantially modified by the e-e interaction. For finite U, the conductance versus epsilon(d) shows a maximum at which the value G(0) is reached, being supported in this case by the two channels (bonding and antibonding); the relative weight of each channel depends on the actual value of the e-e interaction. In the limit epsilon(d)=-infinity, the conductance is supported only by the AB channel (as in the noninteracting case), but it is always smaller than G(0). While the mechanism underlying these results is mainly one body for small U, the Kondo effect and quantum interference come into play at large U. The effects of the e-e interaction increase significantly as the leads-dots coupling decreases, in particular, the range over which the conductance is non-negligible is significantly narrowed. The possible implications on a physically related system, a hydrogen molecule longitudinally bridging two Pt electrodes, are discussed.