Tunable hyperbolic Landau-level polaritons in charge-neutral graphene nanoribbon metasurfaces

TL;DR

This paper introduces a new type of tunable quantum polaritons in charge-neutral graphene nanoribbons under magnetic fields, exhibiting hyperbolic dispersion and topological transitions, with potential applications in quantum sensing and computing.

Contribution

It demonstrates the design of a quantum metasurface supporting tunable hyperbolic Landau-level polaritons with controllable topology and wavefront shaping capabilities.

Findings

Quantum polaritons in charge-neutral graphene can have hyperbolic dispersion.

The topology of isofrequency curves can be tuned from closed to open.

Topological transition leads to canalization phenomena.

Abstract

Magnetized charge-neutral graphene supports collective hybrid electronic excitations - polaritons - which have quantum origin. In contrast to polaritons in doped graphene, which arise from intraband electronic transitions, those in charge-neutral graphene originate from interband transitions between Landau levels, enabled by the applied magnetic field. Control of such quantum polaritons and shaping their wavefronts remains totally unexplored. Here we design an artificial two-dimensional quantum material formed by charge-neutral graphene nanoribbons exposed to an external magnetic field. In such metasurface, quantum polaritons acquire a hyperbolic dispersion. We find that the topology of the isofrequency curves of quantum hyperbolic magnetoexciton polaritons excited in this quantum material can change, so that the shape of isofrequency curves transforms from a closed to open one by tuning the external magnetic field strength. At the topological transition, we observe canalization phenomena, consisting of the propagation of all the polaritonic plane waves in the continuum along the same direction when excited by a point source. From a general perspective, our fundamental findings introduce a novel type of actively-tunable quantum polaritons with hyperbolic dispersion and can be further generalized to other types of quantum materials and polaritons in them. In practice, quantum hyperbolic polaritons can be used for applications related to quantum sensing and computing.