# Tuning quantum non-local effects in graphene plasmonics

## TL;DR

This study uses graphene plasmons and engineered environments to experimentally probe the quantum electronic response of graphene at short wavelengths, revealing detailed quantum effects and matching theoretical models.

## Contribution

It introduces an experimental approach to measure the full spatiotemporal quantum response of graphene's electron liquid using near-field imaging of propagating plasmons.

## Key findings

- Match between experiments and quantum Dirac electron gas theory
- Identification of three quantum effects influencing response
- Potential to determine full electron system response

## Abstract

The response of an electron system to electromagnetic fields with sharp spatial variations is strongly dependent on quantum electronic properties, even in ambient conditions, but difficult to access experimentally. We use propagating graphene plasmons, together with an engineered dielectric-metallic environment, to probe the graphene electron liquid and unveil its detailed electronic response at short wavelengths.The near-field imaging experiments reveal a parameter-free match with the full theoretical quantum description of the massless Dirac electron gas, in which we identify three types of quantum effects as keys to understanding the experimental response of graphene to short-ranged terahertz electric fields. The first type is of single-particle nature and is related to shape deformations of the Fermi surface during a plasmon oscillations. The second and third types are a many-body effect controlled by the inertia and compressibility of the interacting electron liquid in graphene. We demonstrate how, in principle, our experimental approach can determine the full spatiotemporal response of an electron system.