Akhmerov A R, Beenakker C W J
Instituut-Lorentz, Universiteit Leiden, P.O. Box 9506, 2300 RA Leiden, The Netherlands.
Phys Rev Lett. 2007 Apr 13;98(15):157003. doi: 10.1103/PhysRevLett.98.157003. Epub 2007 Apr 12.
Because the valleys in the band structure of graphene are related by time-reversal symmetry, electrons from one valley are reflected as holes from the other valley at the junction with a superconductor. We show how this Andreev reflection can be used to detect the valley polarization of edge states produced by a magnetic field. In the absence of intervalley relaxation, the conductance GNS=(2e2/h)(1-cosTheta) of the junction on the lowest quantum Hall plateau is entirely determined by the angle Theta between the valley isospins of the edge states approaching and leaving the superconductor. If the superconductor covers a single edge, Theta=0 and no current can enter the superconductor. A measurement of GNS then determines the intervalley relaxation time.
由于石墨烯能带结构中的能谷通过时间反演对称性相关联，来自一个能谷的电子在与超导体的结处会被反射为来自另一个能谷的空穴。我们展示了这种安德列夫反射如何可用于检测由磁场产生的边缘态的能谷极化。在不存在能谷间弛豫的情况下，最低量子霍尔平台上结的电导(G_{NS}=(2e^2/h)(1 - \cos\Theta))完全由接近和离开超导体的边缘态的能谷同位旋之间的夹角(\Theta)决定。如果超导体覆盖单个边缘，(\Theta = 0)且没有电流能进入超导体。对(G_{NS})的测量随后可确定能谷间弛豫时间。
