Valley-resolved transport in zigzag graphene nanoribbon junctions

Applying the transfer matrix and Green's function methods, we study the valley-resolved transport properties of zigzag graphene nanoribbon (ZGNR) junctions. The width of the left and right ZGNRs are N-L and N-R, and N-L >= N-R. The step/dip positions of the conductance G, the intravalley transmission coefficients (T-KK and T-K'K'), and the valley polarization efficiency P-KK' correspond to the subband edges of the right/left ZGNR that are controlled by N-R/N-L. The intervalley transmission coefficients (T-KK' and T-K'K) exhibit peaks at most of the subband edge of the left and right ZGNRs. In the bulk gap of the right ZGNR, T-KK' =T-K'K=0, and P-KK' = +/- 1, the valley polarization is well preserved. As N-R increases, the energy region for P-KK' = +/- 1 decreases. When N-L is fixed and N-R decreases, G, T-KK, T-K'K' and P-KK' exhibit more and more dips, and the peaks of T-KK cent'(T-K'K) become more and more high, especially when (N-L - N-R)/2 is odd. These characters are quite useful for manipulating the valley dependent transport properties of carriers in ZGNR junctions by modulating N-L or N-R, and our results are helpful to the design of valleytronics based on ZGNR junctions.

Automated summary

This study investigates the valley-resolved transport properties of zigzag graphene nanoribbon (ZGNR) junctions using the transfer matrix and Green's function methods. It is found that by adjusting the width of ZGNRs, the valley polarization efficiency and transmission coefficients can be controlled, which has potential applications in manipulating carrier transport properties at ZGNR junctions.