Tunable interband and intraband plasmons in twisted double bilayer graphene

TL;DR

This paper reports the discovery of tunable, long-lived terahertz plasmons in twisted double bilayer graphene, with their properties influenced by Van Hove singularities, Berry connections, and external tuning parameters.

Contribution

It introduces the existence and tunability of both interband and intraband plasmons in twisted double bilayer graphene, highlighting their universal dispersion and dependence on system parameters.

Findings

Interband plasmons originate from Van Hove singularities and Berry connections.

The interband plasmon gap is determined by the Van Hove singularity.

Intraband plasmons become flat at large momentum and are tunable via electric field and doping.

Abstract

Flat bands in twisted moire superlattices support a variety of topological and strongly correlated phenomena along with easily tunable electrical and optical properties. Here, we demonstrate the existence of tunable, long-lived, and flat intraband and interband terahertz plasmons in twisted double bilayer graphene. We show that the interband plasmons originate from the presence of a Van Hove singularity in the joint density of states and a finite Berry connection between the pair of bands involved. We find that the gapped interband plasmon mode has a universal dispersion, and the plasmon gap is specified by the location of the Van Hove singularity in the joint density of states. Metallic moire systems support an additional intraband plasmon mode which becomes flat in the large momentum limit because of the influence of the interband correlations. We demonstrate that the undamped and flat plasmon modes in moire systems are highly tunable and can be controlled by varying the vertical electric field and electron doping, and they persist over a wide range of twist angles.