Effect of electron-hole inhomogeneity on specular Andreev reflection and Andreev retroreflection in a graphene-superconductor hybrid system
Effect of electron-hole inhomogeneity on specular Andreev reflection and Andreev retroreflection in a graphene-superconductor hybrid system
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DOI：
10.1103/physrevb.83.235403
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发表时间：
2011-06
影响因子：
3.7
通讯作者：
Shu-guang Cheng;Hui Zhang;Qing Sun
中科院分区：
文献类型：
--
作者：
Shu-guang Cheng;Hui Zhang;Qing Sun
最近的实验证实了石墨烯中的电子-空穴不均匀性是一种新型的电荷紊乱，电子和空穴坑相对于狄拉克点的最大能量位移可达到近30 meV。本文主要研究了电子-空穴不均匀性对Andreev反射和Andreev反反射的影响。在四端石墨烯-超导体杂化体系中，我们发现即使在较大的电子-空穴不均匀性（通常为30 meV）下，Andreev系数也几乎不会受到影响，并且区分两个Andreev反射的边界可以很好地保持，尽管电荷水坑的强度W = 30 meV远大于超导体间隙Delta = 1 meV。此外，当电荷坑比超导体间隙大两个数量级时，仍然可以明显地检测到一种特定的安德烈夫反射。为了定量描述边界模糊的程度，引入了一个量D，它测量了能量空间中镜面安德烈夫反射和反向反射之间的交叉区域的宽度。我们证实了边界模糊比电荷水坑强度w要小得多。此外，我们研究了Anderson无序的影响进行比较，发现在这种情况下边界的保持要明显得多。最后，研究了Andreev反射系数的波动。在一个典型的实验电荷坑下，当粒子的能量远离边界时，波动非常小，再次证实了在电子-空穴不均匀性存在的情况下，可以清楚地区分和检测到反向反射和镜面反射。
The electron-hole inhomogeneity in graphene has been confirmed to be a new type of charge disorder by recent experiments, and the largest energy displacement of electron and hole puddles with respect to the Dirac point can reach nearly 30 meV. Here we focus on how the electron-hole inhomogeneity affects the specular Andreev reflection as well as the Andreev retroreflection. In a four-terminal graphene-superconductor hybrid system, we find that the Andreev coefficients can hardly be affected even under a rather large electron-hole inhomogeneity (typically 30 meV), and the boundary distinguishing two Andreev reflections can well hold, although the strength of the charge puddles, W = 30 meV, is much larger than the superconductor gap, Delta = 1 meV. Furthermore, when charge puddles are two orders of magnitude larger than the superconductor gap, a specific kind of Andreev reflection can still be obviously detected. To quantitatively describe what degree of the boundary is blurred, a quantity D is introduced which measures the width of a crossover region between specular Andreev reflection and retroreflection in energy space. We confirm that the boundary blurring is much smaller than the charge puddle strength W. In addition, we study the effect of Anderson disorder for comparison, and we find that the boundary is held much more obviously in this case. Finally, the fluctuations of the Andreev reflection coefficient are studied. Under a typical experimental charge puddle, the fluctuations are very small when the energy of the particles is away from the boundary, again confirming that the retroreflection and specular reflection can be clearly distinguished and detected in the presence of the electron-hole inhomogeneity.