Intrinsic properties of bipolarons in armchair graphene nanoribbons

We performed an investigation concerning bipolaron dynamics in armchair graphene nanoribbons (AGNRs) under the influence of different electric fields and electron–phonon coupling regimes. By studying the response to the electric field, we determined the effective mass and terminal velocity of this quasiparticle in AGNRs. Remarkably, bipolarons in narrower AGNRs move as fast as the ones in conjugated polymers. Our findings pave the way to enhance the understanding of the behavior of charge carriers in graphene nanoribbons

Influence of quasi-particle density over polaron mobility in armchair graphene nanoribbons

An important aspect concerning the performance of armchair graphene nanoribbons (AGNRs) as materials for conceiving electronic devices is related to the mobility of charge carriers in these systems. When several polarons are considered in the system, a quasi-particle wave function can be affected by that of its neighbor provided the two are close enough. As the overlap may affect the transport of the carrier, the question concerning how the density of polarons affect its mobility arises. In this work, we investigate such dependence for semiconducting AGNRs in the scope of nonadiabatic molecular dynamics. Our results unambiguously show an impact of the density on both the stability and average velocity of the quasi-particles. We have found a phase transition between regimes where increasing density stops inhibiting and starts promoting mobility; densities higher than 7 polarons per 45 angstrom present increasing mean velocity with increasing density. We have also established three different regions relating electric field and average velocity. For the lowest electric field regime, surpassing the aforementioned threshold results in overcoming the 0.3 angstrom fs(-1) limit, thus representing a transition between subsonic and supersonic regimes. For the highest of the electric fields, density effects alone are responsible for a stunning difference of 1.5 angstrom fs(-1) in the mean carrier velocity.Funding Agencies|CNPq; CAPES; FAP-DF; CENAPAD-SP; Brazilian Ministry of Planning, Development and Management [005/2016, 11/2016]; DPGU - Brazilian Union Public Defender [066/2016]; FAP-DF [0193.000.942/2015, 193.001.511/2017]</p

Spin-Orbit Effects on the Dynamical Properties of Polarons in Graphene Nanoribbons

The dynamical properties of polarons in armchair graphene nanoribbons (GNR) is numerically investigated in the framework of a two-dimensional tight-binding model that considers spin-orbit (SO) coupling and electron-lattice (e-l) interactions. Within this physical picture, novel polaron properties with no counterparts to results obtained from conventional tight-binding models are obtained. Our findings show that, depending on the systems width, the presence of SO coupling changes the polarons charge localization giving rise to different degrees of stability for the charge carrier. For instance, the joint action of SO coupling and e-l interactions could promote a slight increase on the charge concentration in the center of the lattice deformation associated to the polaron. As a straightforward consequence, this process of increasing stability would lead to a depreciation in the polarons motion by decreasing its saturation velocity. Our finds are in good agreement with recent experimental investigations for the charge localization in GNR, mostly when it comes to the influence of SO coupling. Moreover, the contributions reported here provide a reliable method for future works to evaluate spin-orbit influence on the performance of graphene nanoribbons.Funding Agencies|CNPq; CAPES; FAP-DF; FINATEC; Brazilian Ministry of Planning, Development and Management [005/2016 DIPLA, 11/2016 SEST]; DPGU - Brazilian Union Public Defender [066/2016]; FAP-DF [0193.000.942/2015, 0193.001343/2016]; IFG</p