Transmission eigenvalue distributions in highly conductive molecular junctions

The transport through a quantum-scale device may be uniquely characterized by its transmission eigenvalues τ(n). Recently, highly conductive single-molecule junctions (SMJ) with multiple transport channels (i.e., several τ(n) > 0) have been formed from benzene molecules between Pt electrodes. Transport through these multichannel SMJs is a probe of both the bonding properties at the lead-molecule interface and of the molecular symmetry.

We use a many-body theory that properly describes the complementary wave-particle nature of the electron to investigate transport in an ensemble of Pt-benzene-Pt junctions. We utilize an effective-field theory of interacting π-electrons to accurately model the electrostatic influence of the leads, and we develop an ab initio tunneling model to describe the details of the lead-molecule bonding over an ensemble of junction geometries. We also develop a simple decomposition of transmission eigenchannels into molecular resonances based on the isolated resonance approximation, which helps to illustrate the workings of our many-body theory, and facilitates unambiguous interpretation of transmission spectra.

We confirm that Pt-benzene-Pt junctions have two dominant transmission channels, with only a small contribution from a third channel with τ(n) << 1. In addition, we demonstrate that the isolated resonance approximation is extremely accurate and determine that transport occurs predominantly via the HOMO orbital in Pt-benzene-Pt junctions. Finally, we show that the transport occurs in a lead-molecule coupling regime where the charge carriers are both particle-like and wave-like simultaneously, requiring a many-body description.