Engineering plasmon modes and their loss in armchair graphene nanoribbons by selected edge-extended defects

Abstract

The effect of edge modification of armchair graphene nanoribbons (AGNRs) on the collective excitations are theoretically investigated. The tight-binding method is employed in conjunction with the dielectric function. Unconventional plasmon modes and their association with the flat bands of the specially designed AGNRs are thoroughly studied. We demonstrate the robust relationship between the novel collective excitations and both the type and period of the edge modification.Additionally, we reveal that the main features displayed in the (momentum, frequency)-phase diagrams for both single-particle and collective excitations of AGNRs can be efficiently tuned by edge-extended defects. Our obtained plasmon modes are found to be analogous to magnetoplasmons associated with collective excitations of Landau-quantized electrons. This work provides a unique way to engineer discrete magnetoplasmon-like modes of AGNRs in the absence of magnetic field. I. INTRODUCTIONGraphene nanoribbons (GNRs) are quasi-one-dimensional systems that present great promise for nanoelectronics, optoelectronics, spintronics and other device applications.Nowadays, GNRs can be synthesized by using various experimental techniques, including either bottom-up [1-9] or top-down [10-16] approaches. Edge defects, which usually appear during the fabrication processes for GNRs, have been shown to modify the fundamental characteristics of targeted materials. Therefore, special attention has been directed toward the edge-modified armchair graphene nanoribbons (AGNRs) because of their versatility, stability and interesting physics, e.g., topological behavior [17,18], band engineering [2], quantum-phase transition [19], and quantum magnetism [20].Collective excitation in a quantum many-body system becomes a critical concept for a deep understanding of the physical properties of materials, such as the optical-absorption spectra [21], fractional-quantum Hall plateaus [22], electronic excitations [23] and decay rates [24,25], to name just a few. In this paper, we will concentrate on plasmons, which result from collective excitations of Coulomb-coupled charged carriers in the conduction or valence bands, and their various effects as well. Plasmon modes are found to be a quantum representative of the charge-density oscillations in lattice structures, as shown in Fig. 1(a), for electrons at the valence-band extrema. In particular, effects of plasmons in graphene play