Floquet Control of Electron and Exciton Transport in Kekul\'e-Distorted Graphene

TL;DR

This paper explores how high-frequency electromagnetic fields influence electron and exciton transport in Kekul'e-distorted graphene, revealing unique tunneling behaviors and potential applications in valleytronics and optoelectronics.

Contribution

It demonstrates the impact of Floquet driving on transport properties and exciton formation in Kekul'e-distorted graphene, highlighting novel topological effects and control mechanisms.

Findings

Almost perfect exciton transmission across barriers at any incident angle.

Suppressed electron transmission due to Kekul'e distortion and irradiation.

Circularly polarized light modifies exciton properties and induces topological behaviors.

Abstract

This work investigates the Floquet dynamics of electrons and excitons (particle-hole pairs) in a Dirac material referred to as Kekul\'e-distorted graphene. Specifically, we examine the role played by a high frequency driving electromagnetic field on the tunneling and blocking by a potential barrier on both the charged single particles as well as the neutral composite particles. We demonstrate that the small effective masses of the electron and hole for the energy spectrum of this Kekul\'e distorted graphene leads to practically almost perfect transmission across a symmetric potential barrier for any angle of incidence of impinging excitons. However, this unexpected Klein paradox for excitons does not hold for the single-particle electrons. The reduced total transmission of electron due to Kekul\'e distortion is more suppressed due to irradiation. Additionally, we calculate and investigate the exciton binding energy since the quantum tunneling of a bound electron-hole pair across a potential barrier is governed by its mass measured in the center of mass and binding energy of the composite pair. Thus, irradiation with circularly polarized light fundamentally modifies exciton formation, coherence and transport properties, thereby producing unusual topological behaviors. These behaviors are unlike conventional Dirac materials. Possible technical applications of the results arising from our investigation include valleytronics due to the folding of the valleys, thereby making intervalley coupling feasible. Other practical applications include optoelectronics due to Floquet tuning of energy spectrum and transport properties.