Abstract
In addition to electron charge and spin, novel materials host another degree of freedom, the valley. For a junction composed of valley filter sandwiched by two normal terminals, we focus on the valley efficiency under disorder with two valley filter models based on monolayer and bilayer graphene. Applying the transfer matrix method, valley resolved transmission coefficients are obtained. We find that: (i) under weak disorder, when the line defect length is over about , it functions as a perfect channel (quantized conductance) and valley filter (totally polarized); (ii) in the diffusive regime, combination effects of backscattering and bulk states assisted intervalley transmission enhance the conductance and suppress the valley polarization; (iii) for very long line defect, though the conductance is small, polarization is indifferent to length. Under perpendicular magnetics field, the characters of charge and valley transport are only slightly affected. Finally we discuss the efficiency of transport valley polarized current in a hybrid system.
Highlights
Electron manipulation in solid state physics reveals the nature of materials and provides potential application in nano-devices
Theoretical results indicate that the linear conductance through a line defect in bilayer graphene should be 2G0 (G0 = 2e2/h the quantum conductance), the experiment detected value is smaller, indicating that the ideal value is affected by disorder and the limited sample size
The valley filter was first proposed by Rycerz et al,[21] which is composed of a narrow graphene nanoribbon sandwiched by two ribbons of large width
Summary
Electron manipulation in solid state physics reveals the nature of materials and provides potential application in nano-devices. We investigate the generation of valley resolved kink states in line junctions based on monolayer and bilayer graphene models. In the clean limit, when the length of the line defect is over 15nm, both models serves well as valley filter with quantized conductances G (G = G0 for monolayer graphene model and G = 2G0 for bilayer graphene model without spin degeneracy) and nearly total valley polarized. The main results are given, including i) how long a line defect is needed to function as a perfect valley filter; ii) the performances of monolayer and bilayer graphene model under disorder; iii) the performance of valley filter for different length; iv) the efficiency of injecting valley polarized current into normal monolayer graphene.
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