Plasmonic Light Emission in Tunneling Systems

Plasmonic light emission in tunnelling systems arises when electrons traverse nanoscale gaps between conductive surfaces, losing energy by exciting confined plasmonic modes. In metal–insulator–metal junctions or tip–substrate nanocavities, inelastic electron tunnelling couples to localized surface plasmons, which can radiate photons into the far field or launch propagating surface plasmon polaritons. Atomic‐scale control of the gap and emitter position enables tuning of coupling strengths, spectral profiles and quantum interference phenomena such as Fano resonances and photonic Lamb shifts. These effects underpin developments in single‐molecule electroluminescence, deterministic energy transfer, on‐chip plasmonic circuitry and ultracompact nanoscale light sources. Understanding the interplay of electronic structure, emitter state lifetimes and cavity enhancements is crucial for applications in quantum optics, nanoscale metrology and integrated optoelectronics.

Research from Nature Portfolio

Recent investigations have measured charge‐state lifetimes of single molecules decoupled by ultrathin insulating films using scanning tunnelling microscopy. By approaching the tip under resonant conditions and monitoring current saturation, researchers quantified anion and cation lifetimes, revealing how level alignment at the metal–insulator interface governs exciton dynamics and electroluminescence efficiency.

Another study presented a fully experimental method to disentangle radiative and non‐radiative plasmonic modes in an atomically defined nanocavity under tunnelling excitation. By combining luminescence spectra with elastic current measurements and electromagnetic simulations, the frequency‐dependent radiative Purcell enhancement was determined as a function of atomic‐scale gap variations.

Seminal work on coherent molecule–nanocavity coupling achieved sub‐nanometre positioning of a single emitter within a plasmonic gap. Evolution of Fano lineshapes and photonic Lamb shifts in tunnelling‐induced luminescence spectra revealed coupling strengths up to tens of millielectronvolts and photonic shifts of several millielectronvolts, paving the way for atomic-scale control of quantum interference and field–matter interactions.

Plasmonic Light Emission in Tunneling Systems publication trend

The graph below shows the total number of articles in plasmonic light emission in tunneling systems across all publications each year (not limited to Nature Index journals).

Technical terms

Inelastic electron tunnelling: Electron passage through a barrier accompanied by energy loss to excitations such as plasmons.

Surface plasmon polariton (SPP): Coupled oscillations of electrons and electromagnetic fields confined at a metal–dielectric interface.

Scanning tunnelling microscope (STM): Instrument that uses a sharp conductive tip to inject electrons into a surface with atomic precision.

Purcell effect: Modification of an emitter’s spontaneous emission rate due to its electromagnetic environment.

Fano resonance: Asymmetric spectral feature arising from interference between discrete and continuum excitation pathways.

Nanocavity: Sub-wavelength volume formed between metallic structures that supports highly confined optical modes.

References

1. Charge-state lifetimes of single molecules on few monolayers of NaCl. Nature Communications (2023).
2. Unveiling the radiative local density of optical states of a plasmonic nanocavity by STM. Nature Communications (2020).
3. Sub-nanometre control of the coherent interaction between a single molecule and a plasmonic nanocavity. Nature Communications (2017).
4. Activating the Fluorescence of a Ni(II) Complex by Energy Transfer. Journal of the American Chemical Society (2024).
5. Mapping Lamb, Stark, and Purcell Effects at a Chromophore-Picocavity Junction with Hyper-Resolved Fluorescence Microscopy. Physical Review X (2022).
6. Efficient Surface Plasmon Polariton Excitation and Control over Outcoupling Mechanisms in Metal–Insulator–Metal Tunneling Junctions. Advanced Science (2020).