Study of conductance in graphene nanochannels for symmetric and asymmetric junction configurations

Abstract

The transport properties of graphene nanochannels have been studied for symmetric and asymmetric junction configurations using an open-source Python-based tool “Kwant”. In the design process, the arrangement of a narrow channel connected between the two wide graphene nanoribbons appeals to shapes like U and H. Both zigzag (ZNR) and armchair graphene nanoribbons (AGNR) are considered as case studies, and the effect of side junctions on the conductance and density of states are analysed as a function of nanochannel width (W_C). It is observed that, in all the shapes as W_C increases the conductance enhances around the zero Fermi energy. Unity conductance is achieved with W_C = 8, 12, and 16 atoms for unmodulated ZNR channels of length 60 Å. However, for U- and H-shapes with narrow channels (W_C = 8 or 12 atoms), the scattering effect is prominent at the junction leading to not only in reduction but also fluctuation of the conductance. A wider channel (W_C = 16 atoms), reduces the scattering effect and leads to unity conductance. On the other hand, for the AGNR-based U-shaped structure although the channels with W_C = 23, 29, and 35 atoms satisfy metallic conditions (W_C = 3p + 2), the conductance is still zero. However, for the H-shaped structure, the channel with W_C = 35 atoms possess unity conductance. Moreover, studying the effect of asymmetry in the junction alignment of the channel in the H-shape, the conductance fluctuates for the AGNR case but remains unchanged for the ZNR case.