Collective Plasmon-Molecule Excitations in Nanojunctions: Quantum Consideration

We use a pseudoparticle nonequilibrium Green function approach to study the coupling between plasmons and molecular excitons in nonequilibrium molecular junctions. This method is shown to be especially convenient for the calculation of the plasmon absorption spectrum of hybrid plasmon-exciton systems where coherent electron and energy transfer processes and strong system interactions play an important role. The formalism treats the intramolecular interactions and plasmon-exciton coupling exactly, going beyond the standard tool of molecular electronics - the nonequilibrium Green function. We demonstrate the sensitivity of the molecule-plasmon Fano resonance to junction bias, Coulomb repulsion, and intramolecular exciton coupling. We also compare our prediction for non-linear optical effects to previous mean-field equilibrium studies of isolated hybrid plasmon-exciton systems, and demonstrate the advantage of our approach. This study opens a way to deal with strongly interacting plasmon-exciton systems in nonequilibrium molecular devices.