Mechanism of Bimodal Light Emission in a Molecule-Mediated Scanning Tunneling Microscopy Junction

We simulate the light emission from C60 films driven by the tunneling electrons injected from a scanning tunneling microscope (STM) tip. Considering a model Hamiltonian which contains electron–photon and exciton–plasmon interactions, the emission spectrum is calculated by using the nonequilibrium Green’s function method. Our simulations indicate that the two emission channels induced by the exciton and gap plasmon are almost independent in such a system, which gives rise to a bimodal-shaped light emission, and the emission ratio between the two channels can be controlled by varying the position of the STM tip. These results are consistent with recent experimental observations. Furthermore, the light emission is shown to be sensitive to the energy detuning and the bias voltage. The connection between bimodal and typical Fano line shape is also clarified. In particular, the stronger Purcell effect that is manifested by a significant enhancement of the spectrum in weak molecule–substrate coupling regime can ...