Controlling gap plasmons with quantum resonances

• Published in: Physical review. B 2018-10, Vol.98 (15), p.155426, Article 155426
• Main Authors: Marinica, D C, Silkin, V M, Kazansky, A K, Borisov, A G
• Format: Article
• Language: English
• Subjects: Density functional theory; Electrodynamics; Electron states; Electron transport; Electron tunneling; Holes (electron deficiencies); Metal surfaces; Plasmonics; Plasmons; Quantum wells; Time dependence
• ISSN: 2469-9950; 2469-9969
• DOI: 10.1103/PhysRevB.98.155426

We use classical electrodynamics, time-dependent density functional theory, and random-phase approximation to study the gap plasmons propagating in the nm-wide gap between metal surfaces. Particular emphasis is given to the quantum effects emerging when the junction is functionalized with a nanostructure supporting unoccupied gap localized electronic states. With the example of a quantum well (QW) introduced in the junction we show that the optically assisted electron transport across the junction via the gateway QW localized electronic states might strongly affect the lifetime and the propagation length of the gap plasmon. The coupling to the single-particle electron-hole excitations from occupied electronic states at metal surfaces into the QW-localized electronic states provides an efficient decay channel of the gap plasmon mode. Different from the through-gap electron tunneling discussed in the plasmonics literature, the electron transport involving the gateway electronic state is characterized by the threshold behavior with plasmon frequency. As a consequence, the dynamics of the gap plasmon can be controlled by varying the binding energy of the QW-localized electronic state. In more general terms, our results demonstrate strong sensitivity of the gap plasmons to the optically assisted electron transport properties of the junction which opens further perspectives in design of nanosensors and integrated active optical devices.