Symmetry aspects of spin-filtering in molecular junctions: hybridization and quantum interference effects

Abstract

Control and manipulation of electric current and, especially, its degree of spin polarization (spin filtering) across single molecules are currently of great interest in the field of molecular spintronics. We explore one possible strategy based on the modification of nanojunction symmetry which can be realized, for example, by a mechanical strain. Such modification can activate new molecular orbitals which were inactive before due to their orbital mismatch with the electrode's conduction states. This can result in several important consequences such as (i) quantum interference effects appearing as Fano-like features in electron transmission and (ii) the change in molecular level hybridization with the electrode's states. We argue that the symmetry change can affect very differently two majority- and minority-spin conductances and thus alter significantly the resulting spin-filtering ratio as the junction symmetry is modified. We illustrate the idea for two basic molecular junctions: Ni/benzene/Ni (perpendicular vs tilted orientations) and Ni/Si chain/Ni (zigzag vs linear chains). In both cases, one highest occupied molecular orbital (HOMO) and one lowest unoccupied molecular orbital (LUMO) (out of HOMO and LUMO doublets) are important. In particular, their destructive interference with other orbitals leads to dramatic suppression of majority-spin conductance in low-symmetry configurations. For a minority-spin channel, on the contrary, the conductance is strongly enhanced when the symmetry is lowered due to an increase in hybridization strength. We believe that our results may offer a potential route for creating molecular devices with a large on-off ratio of spin polarization via quantum interference effects.

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Cited by in corpus (10)

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• Highly conductive and complete spin filtering of nickel atomic contacts in a nitrogen atmosphere
• Giant anisotropic magnetoresistance through a tilted molecular $\pi$-orbital
• Many-body quantum interference route to the two-channel Kondo effect: Inverse design for molecular junctions and quantum dot devices
• Electrode effects on the observability of destructive quantum interference in single-molecule junctions
• Tuning spin filtering by anchoring groups in benzene derivative molecular junctions
• Conductance zeros in complex molecules and lattices from the interference set method
• Current shot noise in atomic contacts: Fe and FeH${}_2$ between Au electrodes
• Robust conductance zeroes in graphene quantum dots and other bipartite systems