Electron transport properties of graphene nanoribbons with Gaussian deformation

Gaussian deformation in graphene structures exhibits an interesting effect in which flower-shaped confinement states are observed in the deformed region [Carrillo-Bastos et al., Phys. Rev. B 90, 041411 (2014)]. To exploit such a deformation for various applications, tunable electronic features including a band-gap opening for semimetallic structures are expected. Besides, the effects of disorders and external excitations also need to be considered. In this work, we present a systematic study on quantum transport of graphene ribbons with Gaussian deformation. Different levels of deformation are explored to find a universal behavior of the electron transmission. Using a tight-binding model in combination with nonequilibrium Green's-functions formalism, we show that the first plateau of the transmission of semimetallic armchair ribbons is just weakly affected in the case of small Gaussian deformations. However, significant large Gaussian bumps can induce a strong drop of this plateau and a transport gap is formed. The transmission at zero energy is found to decrease exponentially with increasing the size of the Gaussian bump. Moreover, the gap of semiconducting ribbons is enlarged with large deformations. The opening or the widening of the transport gap in large deformed armchair structures is interpreted by a formation of a spatially three-zone behavior of the hopping profile. On the other hand, a transport gap is not observed in zigzag ribbons regardless of the size of Gaussian bumps. This behavior is due to the strong localization of edge states at the energy point E = 0. Furthermore, it unveils the opposite effect of vertical electric fields $+{\mathbit{E}}_{z}$ and $\ensuremath{-}{\mathbit{E}}_{z}$, stemming from the breaking of the mirror symmetry. Additionally, it is also pointed out that the electronic behavior of a Gaussian deformed ribbon including edge roughness is dominated by the characteristics of the edge-roughness effect with strong Anderson-type localized states reflected by sharp peaks in the transmission profile.