Lateral plasmonic crystals: Tunability, dark modes, and weak-to-strong coupling transition

TL;DR

This paper investigates the tunable band structure of lateral plasmonic crystals in a 2D electron gas, revealing dark modes, coupling transitions, and experimental validation of the theoretical model using terahertz transmission.

Contribution

It introduces a comprehensive theory describing mode coupling and transition regimes in gate-controlled lateral plasmonic crystals, supported by experimental evidence.

Findings

Identification of bright and dark plasmonic modes in the crystal

Observation of weak-to-strong coupling transition with increased density modulation

Experimental validation of the theoretical model with terahertz transmission data

Abstract

We study transmission of the terahertz radiation through a two-dimensional electron gas with a concentration controlled by grating gate electrodes. Voltage applied to these electrodes creates a lateral plasmonic crystal with a gate-tunable band structure. We find that only a part of plasmonic modes of such a crystal is seen in the transmission spectrum for the case of homogeneous excitation (so-called bright modes), while there also exist dark modes which show up only in a case of inhomogeneous excitation. We develop a theory that describes both weak- to strong- coupling transition in the crystal with increasing depth of the density modulation and a transition from resonant to super-resonant regime with increasing quality factor of the structure. We discuss very recent experiment, where transmission of the terahertz radiation through GaN/AlGaN based grating gate periodic structures was studied. We argue that this experiment represents an evidence of formation of the lateral plasmonic crystal with the band structure fully controlled by the gate electrodes, in a full agreement with developed theory