Phase transition of polarons in bilayer graphene nanoribbons

Abstract

Stacking graphene nanoribbons (GNRs) is the natural path to obtain semiconductors with exotic quantum phenomena by manipulating the interlayer coupling. Recently, a report demonstrated that, during charge transport, interlayer coupling significantly affects the phonon breathing modes. Therefore, a reliable physical description of charged carriers must explicitly address the coupling nature of the electronic and lattice phenomena. In this work, we gauge the influence of interlayer coupling (t⊥) on the formation of charged carriers in a bilayer of an armchair graphene nanoribbon using a model Hamiltonian with electron-phonon coupling. We find different quasiparticle solutions depending on the t⊥ magnitude. As it increases, the carrier’s charge progressively delocalizes along the layers, resulting in two interlayer polaron morphologies: the non-symmetric (0 meV < t⊥≤ 45 meV) and the symmetric (t⊥> 45 meV). These solutions also manifest in the band structure through first-order electronic phase transitions in the intragap states with a significant energy shift of about 0.3 eV. Consequently, the carrier’s mobility and effective mass are expected to be highly sensitive to t⊥, suggesting that mechanical stress can regulate the mechanism. The findings extend to other GNR bilayers, potentially inspiring the development of novel nanoelectronics based on highly confined stacked systems.

Width effects on bilayer graphene nanoribbon polarons

“…The localized charge accumulation is the polaron charge profile, which is known to be coupled with a local lattice distortion. 37 The presence of the interlayer coupling makes the two layers share charge. In other words, there is charge accumulation in layers A and B.…”

“…That outcome is expected, caused by the continuous hybridization of the orbitals due to the layer proximity promoted by t > . 37 The behavior of the frontier orbitals is of special relevance, calling for a direct look. the interlayer coupling strength.…”

“…Detailed descriptions regarding the modeling and its implementation are presented in previous works. 28,31,[37][38][39][40] The modeling consists of identifying the fundamental physical interactions to describe the GNRs. In a low-energy regime, 23 excitation energies are not high enough to break the binding energy of s-electrons.…”

“…Here, we adopt the same convention from past works. 37,38 The layer with the highest amount of charge (it does not matter which one) will be referred to as layer A. Then, the other one is layer B.…”

“…Its use has allowed the description of electrical conductivity of conjugated polymers [26][27][28][29][30][31][32] and monolayer graphene nanoribbons [33][34][35][36] in terms of charged quasiparticles. More recently, we reported the emergence of different interlayer polaron states 37 and strain-tunable bipolaron stability 38 on ultra-narrow bilayer AGNRs. However, these studies focused on a single nanoribbon width.…”