Sun Qing-Feng, Xie X C
Beijing National Lab for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People's Republic of China.
J Phys Condens Matter. 2009 Aug 26;21(34):344204. doi: 10.1088/0953-8984/21/34/344204. Epub 2009 Jul 27.
We study the electron transport through a graphene nanoribbon-superconductor junction. Both zigzag and armchair edge graphene nanoribbons are considered, and the effects of the magnetic field and disorder on the transport property are investigated. By using the tight-binding model and the non-equilibrium Green's function method, the expressions of the current, conductance, normal tunneling coefficient and Andreev reflection coefficient are obtained. For a clean system and at zero magnetic field, the linear conductance increases approximately in a linear fashion with the on-site energy. In the presence of a magnetic field and a moderate disorder, the linear conductance exhibits plateau structures for both armchair and zigzag edges. The plateau values increase with the width of the graphene ribbon. With a wide sample width, a saturated plateau value of |ν|e(2)/h emerges at the filling factor ν. For a small filling factor, the conductance can reach the saturated value at a small width, but for a high filling factor it requires to have a quite wide sample width to reach the saturated value. In particular, the Andreev reflection coefficient is always at 0.5 after reaching the saturated value, independent of any system parameters. In addition, we also consider the finite bias case, in which the Andreev reflection coefficient and normal tunneling coefficient are studied.
我们研究了电子通过石墨烯纳米带 - 超导体结的输运。考虑了锯齿形和扶手椅形边缘的石墨烯纳米带，并研究了磁场和无序对输运性质的影响。通过使用紧束缚模型和非平衡格林函数方法，得到了电流、电导、正常隧穿系数和安德列夫反射系数的表达式。对于清洁系统且在零磁场下，线性电导随在位能近似呈线性增加。在存在磁场和适度无序的情况下，扶手椅形和锯齿形边缘的线性电导都呈现出平台结构。平台值随石墨烯带的宽度增加。对于较宽的样品宽度，在填充因子ν处会出现饱和平台值|ν|e(2)/h。对于小填充因子，电导在较小宽度时就能达到饱和值，但对于高填充因子，则需要相当宽的样品宽度才能达到饱和值。特别地，安德列夫反射系数在达到饱和值后始终为0.5，与任何系统参数无关。此外，我们还考虑了有限偏压情况，研究了安德列夫反射系数和正常隧穿系数。
