Quantum plasmon enhanced nonlinear wave mixing in graphene nanoflakes*

A distant-neighbor quantum-mechanical method is used to study the nonlinear optical wave mixing in graphene nanoflakes (GNFs), including sum- and difference-frequency generation, as well as four-wave mixing. Our analysis shows that molecular-scale GNFs support quantum plasmons in the visible spectrum region, and significant enhancement of nonlinear optical wave mixing is achieved. Specifically, the second- and third-order wave-mixing polarizabilities of GNFs are dramatically enhanced, provided that one (or more) of the input or output frequencies coincide with a quantum plasmon resonance. Moreover, by embedding a cavity into hexagonal GNFs, we show that one can break the structural inversion symmetry and enable otherwise forbidden second-order wave mixing, which is found to be enhanced by the quantum plasmon resonance too. This study reveals that the molecular-sized graphene could be used in the quantum regime for nanoscale nonlinear optical devices and ultrasensitive molecular sensors.

Automated summary

By using a distant-neighbor quantum-mechanical method, the study explores nonlinear optical effects in graphene nanoflakes, revealing that molecular-scale GNFs support quantum plasmons leading to significant enhancement of nonlinear optical effects. The findings suggest that by resonating at specific frequencies and controlling the structure, one can manipulate nonlinear optical wave mixing phenomena.