Effects of electromagnetic coupling on conductance switching of a gated tunnel junction

Using a combination of density functional theory and quantum master equations approach, we study the effect of electromagnetic (EM) coupling on the nonequilibrium steady-state behavior of a recently introduced gated molecular junction. This junction was demonstrated in a previous publication to exhibit sharp current switching near a certain critical DC field Ez, which induces intramolecular charge transfer, and here, we analyze the steady-state population and current when an AC EM field (EMF) is present. The AC EMF at frequency ω₀ produces pronounced population and current features at gate fields E_z = Ez ± ω₀/ez (where ez is the dipole of the charge-transfer state) and thus allows additional sharp switching capability at lower gate fields. We found that even when EMF is absent, the EM coupling itself changes the overall steady-state population and current distributions because it allows for relaxation via spontaneous emission.