Plasmon-Exciton Strong Coupling in Single-Molecule Junction Electroluminescence

Area of Science:

• Molecular electronics
• Quantum optics
• Nanophotonics

Background:

• Single molecules in metal-molecule-metal junctions can exhibit electroluminescence.
• Light emission typically arises from molecular state transitions, but can involve hybrid light-matter states under strong coupling.
• Understanding strong light-matter interactions in molecular junctions is crucial for novel optoelectronic devices.

Purpose of the Study:

• To investigate electroluminescence in single metal-molecule-metal junctions.
• To explore the role of light-matter coupling in single-molecule light emission.
• To demonstrate strong coupling effects in molecular junctions using simultaneous conductance and electroluminescence measurements.

Main Methods:

• Fabrication of single metal-molecule-metal junctions.
• Simultaneous measurement of electrical conductance and electroluminescence using a scanning tunneling microscope (STM) with a custom spectrometer.
• Experimental analysis combined with electronic structure calculations.

Main Results:

• Evidence for a molecule-electrode interfacial exciton coupled to a junction cavity plasmon was found.
• At resonant transport conditions, the molecular junction acted as a single emitter strongly coupled to the cavity mode.
• Characteristic Rabi splitting of the emission spectrum was observed, indicating strong light-matter coupling.

Conclusions:

• Single-molecule junctions can exhibit strong light-matter coupling.
• The observed Rabi splitting provides the first example of an electroluminescence-driven single-molecule system in the strong coupling regime.
• This work opens new avenues for single-molecule optoelectronics and quantum information processing.