A Novel Viewpoint for Source-drain Driven Current inside Triangular Nanographene : Close Relationship with Magnetic Current

Circular current and induced force in a molecular ring junction

We consider bias-induced circular current in a molecular ring junction. It is natural to define circular current as a component of ring current that acts as a sole source of magnetic flux induced in the ring. Alternatively, the bias-induced circular current can also be determined from the magnetic response of the ring junction to an external flux in the zero-flux limit. This leads to determination of bias-induced circular current without actually calculating the bond currents. We also explore the possibility of circular current-induced force rupturing the covalent bonds in the ring leading to ultimate breakdown of the ring junction. Our calculations underscore the reliability problem posed by the current magnification effect in the molecular ring structures.

A simple molecular orbital treatment of current distributions in quantum transport through molecular junctions

A simple molecular orbital treatment of local current distributions inside single molecular junctions is developed in this paper. Using the first-order perturbation theory and nonequilibrium Green's function techniques in the framework of Hückel theory, we show that the leading contributions to local current distributions are directly proportional to the off-diagonal elements of transition density matrices. Under the orbital approximation, the major contributions to local currents come from a few dominant molecular orbital pairs which are mixed by the interactions between the molecule and electrodes. A few simple molecular junctions consisting of single- and multi-ring conjugated systems are used to demonstrate that local current distributions inside molecular junctions can be decomposed by partial sums of a few leading contributing transition density matrices.

Molecular rectification in triangularly shaped graphene nanoribbons

We present a theoretical study of electron transport in tailored zigzag graphene nanoribbons (ZGNRs) with triangular structure using density functional theory together with the nonequilibrium Green's function formalism. We find significant rectification with a favorite electron transfer direction from the vertex to the right edge. The triangular ZGNR connecting to the electrode with one thiol group at each terminal shows an average rectification ratio of 8.4 over the bias range from -1.0 to 1.0 V. This asymmetric electron transport property originates from nearly zero band gap of triangular ZGNR under negative bias, whereas a band gap opens under positive bias. When the molecule is connected to the electrode by multithiol groups, the current is enhanced due to strong interfacial coupling; however, the rectification ratio decreases. The simulation results indicate that the unique electronic states of triangular ZGNR are responsible for rectification, rather than the asymmetric anchoring groups.