Ring Current and Local Magnetic Fields Influenced by Quantum Interference in Molecular Junctions

It is challenging to produce controllable localized magnetic fields (LMFs) at sub-nanometer scale, which is crucial to the designs of a nanoscale spin filter or spin logic gate. The quantum interferences (QIs) in molecular junctions containing cross and linear π-conjugated structures are studied by applying density functional theory (DFT) and nonequilibrium Green's function method as well as the effects of QIs on ring currents and LMFs produced in molecular junctions. Our calculations unveil that if the molecular junction contains a cyclic segment composed of both cross and linear π-conjugated units, the ring current and controllable nanoscale LMF (>6 mT) can be generated within the cyclic segment. Due to the destructive QI effect of the cross π-conjugated branch, the pathway selection takes place when electrons enter the ring circuit, which results in significant ring current and LMF. Improving the planarity of cyclic structures can effectively enhance ring currents and LMF.