Anisotropic Acoustic Plasmons in Black Phosphorus

TL;DR

This paper explores acoustic plasmons in black phosphorus, revealing their unique dispersion properties and proposing a new resonator design that enhances confinement and efficiency for potential plasmonic devices.

Contribution

It introduces the first detailed theoretical analysis of acoustic plasmons in black phosphorus and proposes a novel resonator design leveraging BP's anisotropy.

Findings

Linear dispersion in armchair direction in mid- and far-infrared regimes

Tighter confinement in zigzag direction prevents clear scaling

Proposed resonator outperforms BP ribbon resonators in confinement and efficiency

Abstract

Recently, it was demonstrated that a graphene/dielectric/metal configuration can support acoustic plasmons, which exhibit extreme plasmon confinement an order of magnitude higher than that of conventional graphene plasmons. Here, we investigate acoustic plasmons supported in a monolayer and multilayers of black phosphorus (BP) placed just a few nanometers above a conducting plate. In the presence of a conducting plate, the acoustic plasmon dispersion for the armchair direction is found to exhibit the characteristic linear scaling in the mid- and far-infrared regime while it largely deviates from that in the long wavelength limit and near-infrared regime. For the zigzag direction, such scaling behavior is not evident due to relatively tighter plasmon confinement. Further, we demonstrate a new design for an acoustic plasmon resonator that exhibits higher plasmon confinement and resonance efficiency than BP ribbon resonators in the mid-infrared and longer wavelength regime. Theoretical framework and new resonator design studied here provide a practical route toward the experimental verification of the acoustic plasmons in BP and open up the possibility to develop novel plasmonic and optoelectronic devices that can leverage its strong in-plane anisotropy and thickness-dependent band gap.