Supercurrent reversal in Josephson junctions based on bilayer graphene flakes
Supercurrent reversal in Josephson junctions based on bilayer graphene flakes
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DOI：
10.1103/physrevb.92.085403
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发表时间：
2015-03
影响因子：
3.7
通讯作者：
B. Rameshti;M. Zareyan;Ali G. Moghaddam
中科院分区：
文献类型：
--
作者：
B. Rameshti;M. Zareyan;Ali G. Moghaddam
研究了超导电极沉积的单层石墨烯片与双层石墨烯片接触时的约瑟夫森效应。结果发现，当电极附着到双层的不同层，约瑟夫森电流是在一个$\pi$状态时，双层区域是未掺杂的，在没有垂直偏置。应用掺杂或偏置的结揭示了$\pi-0$的转变，可以通过改变温度和结的长度来控制。这里的超导反转与铁磁约瑟夫森结非常不同，在铁磁约瑟夫森结中，自旋自由度起着关键作用。我们认为，散射过程伴随着层和亚晶格折射率的变化引起的散射相，其效果随掺杂和偏压。这样的散射相负责$\pi-0$过渡。另一方面，如果两个电极都耦合到薄片的同一层，或者薄片具有AA堆叠而不是公共AB，则结将总是处于$0$状态，因为层或子晶格指数没有改变。
We investigate the Josephson effect in a bilayer graphene flake contacted by two monolayer sheet deposited by superconducting electrodes. It is found that when the electrodes are attached to the different layers of the bilayer, the Josephson current is in a $\pi$ state when the bilayer region is undoped and in the absence of vertical bias. Applying doping or bias to the junction reveals $\pi-0$ transitions which can be controlled by varying the temperature and the junction length. The supercurrent reversal here is very different from the ferromagnetic Josephson junctions where the spin degree of freedom plays the key role. We argue that the scattering processes accompanied by layer and sublattice index change give rise to the scattering phases which their effect varies with doping and the bias. Such scattering phases are responsible for the $\pi-0$ transitions. On the other hand if both of the electrodes are coupled to the same layer of the flake or the flake has AA stacking instead of common AB, the junction will be always in $0$ state since layer or sublattice index is not changed.