Electron transport properties of graphene nanoribbons with Gaussian deformation
Résumé
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 bandgap opening for semi-metallic 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 Non-Equilibrium Green’s Functions formalism, we show that the first plateau of the transmission of semi-metallic 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 the zero energy is found to decrease exponentially with increasing the size of the Gaussian bump. Moreover, the gap of semi-conducting 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 +Ez and -Ez, stemmed by 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.
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