Probing the ultimate plasmon confinement limits with a van der Waals heterostructure.

David Alcaraz Iranzo,Cheng Peng,Romain Parret,Eduardo J C Dias,Itai Epstein,Sébastien Nanot,Dirk R Englund,Jin-Yong Hong,Jing Kong,Johann Osmond,Mark B Lundeberg,Nuno M R Peres,Frank H L Koppens,Dmitri K Efetov

doi:10.1126/science.aar8438

Abstract

The ability to confine light into tiny spatial dimensions is important for applications such as microscopy, sensing, and nanoscale lasers. Although plasmons offer an appealing avenue to confine light, Landau damping in metals imposes a trade-off between optical field confinement and losses. We show that a graphene-insulator-metal heterostructure can overcome that trade-off, and demonstrate plasmon confinement down to the ultimate limit of the length scale of one atom. This is achieved through far-field excitation of plasmon modes squeezed into an atomically thin hexagonal boron nitride dielectric spacer between graphene and metal rods. A theoretical model that takes into account the nonlocal optical response of both graphene and metal is used to describe the results. These ultraconfined plasmonic modes, addressed with far-field light excitation, enable a route to new regimes of ultrastrong light-matter interactions.

Highlights

The basic device geometry consists of graphene as the plasmonic material, encapsulated by atomically thin dielectric materials (h-BN or Al2O3) and covered by a metallic rod array (Fig. 1A) [details on the fabrication processes are provided in [19]]
Screening and coupling of radiation to plasmons in classical 2D electron gases (2DEGs) was previously achieved by using grating-gate field-effecttransistors in the terahertz range [7], a relatively thick barrier layer (~100 nm) prevented the confinement of plasmons to the subnanometer limit, as we report here
Because image charges are induced in the metal, the plasmon mode is analogous to the antisymmetric plasmon mode of two nearby graphene sheets with twice the spacer thickness [8], known as acoustic plasmons, carrying larger momentum than for conventional plasmon resonances in graphene ribbons [(19), section 5.7]

Summary

Introduction

The basic device geometry consists of graphene as the plasmonic material, encapsulated by atomically thin dielectric materials (h-BN or Al2O3) and covered by a metallic rod array (Fig. 1A) [details on the fabrication processes are provided in [19]]. Bringing the metal closer will increase the plasmon screening, which slows down the plasmons, as previously observed with scattering-type scanning near-field optical microscopy [8, 9], and enhances the vertical confinement, as shown for two different dielectric spacer materials and graphene conductivity models (local and nonlocal) (Fig. 1D).

Results

Conclusion