Width effects on bilayer graphene nanoribbon polarons.

Recent progress in nanoelectronics suggests that stacking armchair graphene nanoribbons (AGNRs) into bilayer systems can generate materials with emergent quasiparticle properties. In this context, the impact of width changes is especially relevant. However, its effect on charged carriers remains elusive.

Quasiparticle dynamics by effective [Formula: see text]-field distortion.

Modeling dynamical processes of quasiparticles in low dimensional [Formula: see text]-conjugated systems is challenging due to electron-phonon coupling. We show that this interaction leads to linear potential energy terms in the lattice Lagrangian similar to a local "gravitational" field. The presence of quasiparticles deforms this field in a way analogous to a low-dimension solution of general relativity.

Charge localization and hopping in a topologically engineered graphene nanoribbon.

Graphene nanoribbons (GNRs) are promising quasi-one-dimensional materials with various technological applications. Recently, methods that allowed for the control of GNR's topology have been developed, resulting in connected nanoribbons composed of two distinct armchair GNR families. Here, we employed an extended version of the Su-Schrieffer-Heeger model to study the morphological and electronic properties of these novel GNRs.

Smooth gap tuning strategy for cove-type graphene nanoribbons.

Graphene is a carbon-based material with an extensive range of promising properties. Since it does not present a bandgap, graphene is not suitable for optoelectronic applications. One possible way to open a gap is achieved by reducing graphene to its nanoribbon (GNR) form.

Dynamical Mechanism of Polarons and Bipolarons in Poly(p-Phenylene Vinylene).

Studies on Poly(p-Phenylene Vinylene) (PPV) and derivatives have experienced enormous growth since they were successfully used to fabricate the first efficient prototypes of Polymer Light-Emitting Diodes in the 90s. Despite this rapid progress, understanding the relationship between charge transport and the morphology in these materials remains a challenge. Here, we shed light on the understanding of the transport mechanism of polarons and bipolarons in PPVs by developing a two-dimensional tight-binding approach that includes lattice relaxation effects.

Effective Mass of Quasiparticles in Armchair Graphene Nanoribbons.

Armchair graphene nanoribbons (AGNRs) may present intrinsic semiconducting bandgaps, being of potential interest in developing new organic-based optoelectronic devices. The induction of a bandgap in AGNRs results from quantum confinement effects, which reduce charge mobility. In this sense, quasiparticles' effective mass becomes relevant for the understanding of charge transport in these systems.

Stability conditions of armchair graphene nanoribbon bipolarons.

Graphene nanoribbons are 2D hexagonal lattices with semiconducting band gaps. Below a critical electric field strength, the charge transport in these materials is governed by the quasiparticle mechanism. The quasiparticles involved in the process, known as polarons and bipolarons, are self-interacting states between the system charges and local lattice distortions.

Defective graphene domains in boron nitride sheets.

Novel two-dimensional materials have emerged as hybrid structures that combine graphene and hexagonal boron nitride (h-BN) domains. During their growth process, structural defects such as vacancies and change of atoms connectivity are unavoidable. In the present study, we use first-principle calculations to investigate the electronic structure of graphene domains endowed with a single carbon atom vacancy or Stone-Wales defects in h-BN sheets.

Tuning the electronic structure properties of MoS monolayers with carbon doping.

The structural and electronic properties of MoS sheets doped with carbon line domains are theoretically investigated through density functional theory calculations. It is primarily studied how the system's electronic properties change when different domain levels are considered. These changes are also reflected in the geometry of the system, which acquires new properties when compared to the pristine structure.

Polaron properties in 2D organic molecular crystals: directional dependence of non-local electron-phonon coupling.

In organic molecular crystals, the polaronic hopping model for the charge transport assumes that the carrier lies at one or a small number of molecules. Such a kind of localization suffers the influence of the non-local electron-phonon (e-ph) interactions associated with intermolecular lattice vibrations. Here, we developed a model Hamiltonian for numerically describing the role played by the intermolecular e-ph interactions on the stationary and dynamical properties of polarons in a two-dimensional array of molecules.

Bipolaron Dynamics in Graphene Nanoribbons.

Graphene nanoribbons (GNRs) are two-dimensional structures with a rich variety of electronic properties that derive from their semiconducting band gaps. In these materials, charge transport can occur via a hopping process mediated by carriers formed by self-interacting states between the excess charge and local lattice deformations. Here, we use a two-dimensional tight-binding approach to reveal the formation of bipolarons in GNRs.

Same Charge Polaron and Bipolaron Scattering on Conducting Polymers.

We study the dynamics of scattering of two positive polarons moving toward each other with parallel spins and of a polaron and a bipolaron both with positive charges and different velocities, in single chains of cis-polyacetylene and polyparaphenylene. We use the Su-Schrieffer-Heeger model with Hubbard extensions solved within of the time-dependent Hartree-Fock approximation to account for electron-electron interactions, developed over a hexagonal lattice. The main results are elastic scattering in most cases.

Stationary polaron properties in organic crystalline semiconductors.

Polarons play a crucial role in the charge transport mechanism when it comes to organic molecular crystals. The features of their underlying properties - mostly the ones that directly impact the yield of the net charge mobility - are still not completely understood. Here, a two-dimensional Holstein-Peierls model is employed to numerically describe the stationary polaron properties in organic semiconductors at a molecular scale.

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.

Charge Carrier Scattering in Polymers: A New Neutral Coupled Soliton Channel.

The dynamical scattering of two oppositely charged bipolarons in non-degenerate organic semiconducting lattices is numerically investigated in the framework of a one-dimensional tight-biding-Hubbard model that includes lattice relaxation. Our findings show that it is possible for the bipolaron pair to merge into a state composed of a confined soliton-antisoliton pair, which is characterized by the appearance of states within less than 0.1 eV from the Fermi level.

Dynamic Formation of Bipolaron-Exciton Complexes in Conducting Polymers.

The recombination dynamics of two oppositely charged bipolarons within a single polymer chain is numerically studied in the scope of a one-dimensional tight-binding model that considers electron-electron and electron-phonon (e-ph) interactions. By scanning among values of e-ph coupling and electric field, novel channels for the bipolaron recombination were yielded based on the interplay between these two parameters. The findings point to the formation of a compound species formed from the coupling between a bipolaron and an exciton.

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 system's width, the presence of SO coupling changes the polaron's charge localization giving rise to different degrees of stability for the charge carrier.

Bond length pattern associated with charge carriers in armchair graphene nanoribbons.

The geometry configuration of charged armchair graphene nanoribbons (AGNRs) is theoretically investigated in the framework of a two-dimensional tight-binding model that includes lattice relaxation. Our findings show that the charge distribution and, consequently, the bond length pattern is dependent on the parity of the nanoribbon width. In this sense, the lattice distortions decrease smoothly for increasingly wider GNRs.

Bloch oscillations in organic and inorganic polymers.

The transport of polarons above the mobility threshold in organic and inorganic polymers is theoretically investigated in the framework of a one-dimensional tight-binding model that includes lattice relaxation. The computational approach is based on parameters for which the model Hamiltonian suitably describes different polymer lattices in the presence of external electric fields. Our findings show that, above critical field strengths, a dissociated polaron moves through the polymer lattice as a free electron performing Bloch oscillations.

Polaron and bipolaron stability on paraphenylene polymers.

Polyparaphenylene is the prototypical conjugated polymer containing phenyl rings and its properties are good references for a family of derived polymers. We investigate the structure, stability, and dynamics of polarons and bipolarons in polyparaphenylene chains under an applied electric field. To do this, we use a bidimensional SSH Hamiltonian model with the Hubbard extension, i.

Electron-phonon coupling effects on intrachain polaron recombination in conjugated polymers.

Based on a one-dimensional Su-Schrieffer-Heeger (SSH) model with electron correlation considered within the extended Hubbard model (EHM), we investigate the role played by electron-phonon coupling constant on intrachain polaron recombination in conjugated polymers. Our results suggest that a competition between external electric field and electron-phonon coupling on defining the behavior of the charge distribution of the system takes place. Whereas increasing electric field plays the role of destabilizing the charge carriers, an increase of the electron-phonon coupling has the opposite effect.

Impact of the Electron-Phonon Interactions on the Polaron Dynamics in Graphene Nanoribbons.

The influence of the electron-phonon (e-ph) interactions on the filed-included polaron dynamics in armchair graphene nanoribbons (GNRs) is theoretically investigated in the scope of a two-dimensional tight-binding model. The results show that the localization of the polaronic charge increases when the strength of e-ph coupling also increases. Consequently, the polaron saturation velocity decreases for higher e-ph coupling strengths.

Low-Temperature Seebeck Coefficients for Polaron-Driven Thermoelectric Effect in Organic Polymers.

We report the results of electronic structure coupled to molecular dynamics simulations on organic polymers subject to a temperature gradient at low-temperature regimes. The temperature gradient is introduced using a Langevin-type dynamics corrected for quantum effects, which are very important in these systems. Under this condition we were able to determine that in these no-impurity systems the Seebeck coefficient is in the range of 1-3 μV/K.

Transport of Polarons in Graphene Nanoribbons.

The field-induced dynamics of polarons in armchair graphene nanoribbons (GNRs) is theoretically investigated in the framework of a two-dimensional tight-binding model with lattice relaxation. Our findings show that the semiconductor behavior, fundamental to polaron transport to take place, depends upon of a suitable balance between the GNR width and the electron-phonon (e-ph) coupling strength. In a similar way, we found that the parameter space for which the polaron is dynamically stable is limited to an even narrower region of the GNR width and the e-ph coupling strength.

Concentration effects on intrachain polaron recombination in conjugated polymers.

The influence of different charge carrier concentrations on the recombination dynamics between oppositely charged polarons is numerically investigated using a modified version of the Su-Schrieffer-Heeger (SSH) model that includes an external electric field and electron-electron interactions. Our findings show that the external electric field can play the role of avoiding the formation of excited states (polaron-exciton and neutral excitation) leading the system to a dimerized lattice. Interestingly, depending on a suitable balance between the polaron concentration and the electric field strength, the recombination mechanism can form stable polaron-excitons or neutral excitations.