Gate tunable light-matter interaction in natural biaxial hyperbolic van der Waals heterostructures

TL;DR

This paper demonstrates active tunability of hyperbolic phonon polaritons in van der Waals heterostructures by integrating graphene with biaxial hyperbolic materials, enabling mid-IR nanophotonic applications with directional control and broad bandwidth.

Contribution

It introduces a method to actively tune hyperbolic phonon polaritons in natural biaxial hyperbolic van der Waals heterostructures using electrostatic gating of graphene.

Findings

Hybrid plasmon-phonon polariton modes are tunable via graphene chemical potential.

Propagation direction-dependent hybridization observed.

Broad operational bandwidth for tunable valley quantum interference.

Abstract

The recent discovery of natural biaxial hyperbolicity in van der Waals crystals, such as $\alpha$-MoO$_3$, has opened up new avenues for mid-IR nanophotonics due to their deep subwavelength phonon-polaritons. However, a significant challenge is the lack of active tunability of these hyperbolic phonon polaritons. In this work, we investigate heterostructures of graphene and $\alpha$-MoO$_3$ for actively tunable hybrid plasmon phonon polariton modes via electrostatic gating in the mid-infrared spectral region. We observe a unique propagation direction dependent hybridization of graphene plasmon polaritons with hyperbolic phonon polaritons for experimentally feasible values of graphene chemical potential. We further report an application to tunable valley quantum interference in this system with a broad operational bandwidth due to the formation of these hybrid modes. This work presents a lithography-free alternative for actively tunable, anisotropic spontaneous emission enhancement using a sub-wavelength thick naturally biaxial hyperbolic materials.