石墨烯波导中电子输运的广义传输矩阵理论
Generalized transfer matrix theory on electronic transport through graphene waveguide
摘要：
在有效质量近似下，石墨烯的电子性质可以用相对论狄拉克方程来描述。在这样的连续模型中，我们研究了通过连接多段不同宽度的扶手椅边缘石墨烯纳米带形成的石墨烯波导的电子传输。通过使用适当的波函数连接条件在结界面，我们推广了传统的传输矩阵方法来制定的石墨烯波导的线性电导的结构参数和入射电子能量。通过与紧束缚计算的比较，我们发现广义传输矩阵方法在计算石墨烯波导的电导谱时，即使在结构复杂、尺寸较大的情况下也能取得较好的效果。计算的电导谱表明，石墨烯波导在狄拉克点周围表现出良好定义的绝缘带，即使所有组成的带段是无间隙的。我们将绝缘带的出现归因于反共振效应，它与位于结肩部区域的边缘态密切相关。此外，这种绝缘带可以通过栅极电压灵敏地移位，这表明石墨烯波导作为电纳米开关的器件应用。
英文摘要：
In the effective mass approximation, electronic property in graphene can be characterized by the relativistic Dirac equation. Within such a continuum model we investigate the electronic transport through graphene waveguides formed by connecting multiple segments of armchair-edged graphene nanoribbons of different widths. By using appropriate wavefunction connection conditions at the junction interfaces, we generalize the conventional transfer matrix approach to formulate the linear conductance of the graphene waveguide in terms of the structure parameters and the incident electron energy. In comparison with the tight-binding calculation, we find that the generalized transfer matrix method works well in calculating the conductance spectrum of a graphene waveguide even with a complicated structure and relatively large size. The calculated conductance spectrum indicates that the graphene waveguide exhibits a well-defined insulating band around the Dirac point, even though all the constituent ribbon segments are gapless. We attribute the occurrence of the insulating band to the antiresonance effect which is intimately associated with the edge states localized at the shoulder regions of the junctions. Furthermore, such an insulating band can be sensitively shifted by a gate voltage, which suggests a device application of the graphene waveguide as an electric nanoswitch.
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