# Experimental demonstration of tunable graphene hyperbolic metamaterial

## TL;DR

This paper demonstrates experimentally how doping graphene in a heterostructure can actively tune its hyperbolic optical properties, enabling dynamic control of dielectric responses for advanced photonic applications.

## Contribution

First experimental demonstration of tunable hyperbolic metamaterials using graphene/dielectric heterostructures with doping control.

## Key findings

- Achieved a wide tunability of dielectric properties via doping
- Verified epsilon-near-zero crossing through spectroscopic measurements
- Demonstrated active control of optical resonances in the metamaterial

## Abstract

Tuning the macroscopic dielectric response on demand holds potential for actively tunable metaphotonics and optical devices. In recent years, graphene has been extensively investigated as a tunable element in nanophotonics. Significant theoretical work has been devoted on the tuning the hyperbolic properties of graphene/dielectric heterostructures, however, until now, such a motif has not been demonstrated experimentally. Here we focus on a graphene/polaritonic dielectric metamaterial, with strong optical resonances arising from the polar response of the dielectric, which are, in general, difficult to actively control. By controlling the doping level of graphene via external bias we experimentally demonstrate a wide range of tunability from a Fermi level of EF = 0 eV to EF = 0.5 eV, which yields an effective epsilon-near-zero crossing and tunable dielectric properties, verified through spectroscopic ellipsometry and transmission measurements.