Bidirectional spin filter in a triple orbital molecule junction by tuning the magnetic field along a single direction.

Metal-molecule-metal junction is considered the basing block and key element of molecular spintronic devices, within which to generate spin polarized currents is one of the most fundamental issues for quantum computation and quantum information. In this paper, by employing a parallel triple orbital molecule junction with large inter-orbital tunneling couplings, we propose theoretically a bidirectional spin filter where both spin-up and spin-down currents could be obtained by simply adjusting the external magnetic field to different regimes along a single direction, and the filtered efficiencies could reach almost 100%. The Zeeman effect and the occupancy switching for the bonding and anti-bonding states are found to be responsible for the spin selective transport. We demonstrate that our scheme is robust for large parameter spaces of the orbital energy level, except the particle-hole symmetric point, and is widely suitable for the strong-, weak-, and non-interacting cases. To implement these problems, we use the Wilson's numerical renormalization group technique to treat such systems.