Quantum mechanical analysis of nonlinear optical response of interacting graphene nanoflakes

TL;DR

This paper introduces a comprehensive quantum-mechanical approach to analyze the linear and nonlinear optical properties of graphene nanoflakes, accounting for all atomic interactions and enabling the study of optical coupling and symmetry effects.

Contribution

The proposed DNQM method improves accuracy over tight-binding models by including all atom interactions, allowing detailed analysis of shape, size, and symmetry influences on GNFs' optical responses.

Findings

Increasing nanoflake size shifts plasmon oscillations to lower frequencies.

Embedding cavities alters symmetry and enables forbidden second-harmonic generation.

The approach captures inter-flake optical coupling beyond tight-binding limitations.

Abstract

We propose a distant-neighbor quantum-mechanical (DNQM) approach to study the linear and nonlinear optical properties of graphene nanoflakes (GNFs). In contrast to the widely used tight-binding description of the electronic states that considers only the nearest-neighbor coupling between the atoms, our approach is more accurate and general, as it captures the electron-core interactions between all atoms in the structure. Therefore, as we demonstrate, the DNQM approach enables the investigation of the optical coupling between two closely separated, but chemically unbound GNFs. We also find that the optical response of GNFs depends crucially on their shape, size, and symmetry properties. Specifically, increasing the size of nanoflakes is found to shift their accommodated quantum plasmon oscillations to lower frequency. Importantly, we show that by embedding a cavity into GNFs, one can change their symmetry properties, tune their optical properties, or enable otherwise forbidden second-harmonic generation processes.