Dynamics and Effective Masses of Polarons and Bipolarons in Bilayer Armchair Graphene Nanoribbons

Abstract

An energy band gap, and consequently semiconducting behavior, can be induced by lateral confinement in graphene nanoribbons. In this case, the charge carrier becomes a quasiparticle characterized by electron–phonon coupling, but its effective mass increases significantly, reaching about twenty-seven times the electron mass (27 me) in armchair graphene nanoribbons with a width of four carbon atoms, which reduces charge transport. When coupling between nanoribbons is introduced, new quasiparticle states emerge. In this work, using an extended Su–Schrieffer–Heeger (SSH) model, we show that the effective mass can be reduced from 27 me to approximately 4 me while preserving the semiconducting character of bilayer systems of different widths and interlayer coupling strengths. We model polarons (and bipolarons) as pairs of coupled particles, calling them “phonon” and “electric charge” and separately estimating their effective masses, as well as the coupling force constant between them, for several interlayer coupling strengths. We estimate the internal oscillation frequencies of these charge carriers, which range from 25 THz to 250 THz, and associate them with possible fingerprints in infrared spectra, as well as with potential applications in the development of infrared emitter or absorber devices.