Single-Photon Emission Mediated by Single-Electron Tunneling in Plasmonic Nanojunctions

Area of Science:

• Quantum Optics
• Condensed Matter Physics
• Nanophotonics

Background:

• Scanning tunneling microscopy (STM) enables single-molecule fluorescence via tunneling currents within a nanoplasmonic cavity.
• Cavity mode electric fields couple with current-induced molecular charge fluctuations, leading to photon excitation.

Purpose of the Study:

• Theoretically investigate single-molecule fluorescence in an STM nanoplasmonic cavity.
• Analyze the system's behavior in the limit of high damping rate (κ) for the cavity mode and arbitrary coupling strength to a single electronic level.

Main Methods:

• Theoretical modeling of photon emission from a single molecule coupled to a nanoplasmonic cavity under STM.
• Analysis of photon statistics (antibunching/bunching) and current-voltage characteristics.
• Investigation of Franck-Condon steps influenced by cavity damping (κ) and temperature (T).

Main Results:

• Photon antibunching observed near the first inelastic threshold for photon emission, indicated by a vanishing second-order photon correlation function.
• Franck-Condon steps in current and emitted light intensity occur at multiples of cavity frequency (ωc), with width determined by κ, not T.
• Strong photon bunching predicted at large bias voltages, proportional to κ/Γ (where Γ is the electronic tunneling rate).

Conclusions:

• Strong coupling to a single electronic level enables current-driven nonclassical light emission.
• The study provides a theoretical framework for understanding and controlling light generation at the nanoscale using STM.