Plexciton

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Plexcitons are hybrid waves that form when excitons in molecules strongly couple with plasmons in metals. Excitons are excited electrons bound to the holes they leave behind, while plasmons are collective oscillations of many electrons. When these two kinds of excitations are linked, they create plexcitons that can move energy directly from one molecule to another, helping exciton energy transfer (EET).

This coupling can carry energy over much longer distances than ordinary transfer. In early studies, plexcitons allowed EET over roughly 20,000 nanometers (about 20 micrometers), compared with ~10 nanometers before. However, the energy flow wasn’t directionally controlled at first.

Topological insulators (TIs) offer a way to guide energy along a preferred path. TIs insulate inside but conduct on their surfaces, so electrons tend to move along the surface. By pairing excitons with plasmons on TI-based structures, researchers aim to create topological plexcitons that steer energy along a single interface.

In experiments, plexcitons emerged at the boundary between an organic molecular layer and a metal film. The two-dimensional band structure showed Dirac cones, and applying a magnetic field with a magneto-optical layer opened a gap between them. This gap hosts one-way, edge-only modes that travel along the interface, protected from scattering.

Plexcitons hold promise for new states of matter and for controlling energy flow at the nanoscale.