Department of Physics and Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA 94305, USA.
National Graphene Institute, University of Manchester, Manchester M13 9PL, UK.
Science. 2016 Sep 30;353(6307):1526-1529. doi: 10.1126/science.aaf1095.
Rational design of long-period artificial lattices yields effects unavailable in simple solids. The moiré pattern in highly aligned graphene/hexagonal boron nitride (h-BN) heterostructures is a lateral superlattice with high electron mobility and an unusual electronic dispersion whose miniband edges and saddle points can be reached by electrostatic gating. We investigated the dynamics of electrons in moiré minibands by measuring ballistic transport between adjacent local contacts in a magnetic field, known as the transverse electron focusing effect. At low temperatures, we observed caustics of skipping orbits extending over hundreds of superlattice periods, reversals of the cyclotron revolution for successive minibands, and breakdown of cyclotron motion near van Hove singularities. At high temperatures, electron-electron collisions suppress focusing. Probing such miniband conduction properties is a necessity for engineering novel transport behaviors in superlattice devices.
长周期人工晶格的合理设计产生了简单固体中无法获得的效果。高度取向的石墨烯/六方氮化硼（h-BN）异质结构中的莫尔图案是一种具有高迁移率和异常电子色散的横向超晶格，其能带边缘和鞍点可以通过静电门控来实现。我们通过测量磁场中相邻局部接触之间的弹道输运，研究了莫尔微带中的电子动力学，这被称为横向电子聚焦效应。在低温下，我们观察到扩展到数百个超晶格周期的跳跃轨道焦散线，连续微带中环流旋转的反转，以及范霍夫奇点附近回旋运动的崩溃。在高温下，电子-电子碰撞会抑制聚焦。探测这种微带传导特性是在超晶格器件中实现新型传输行为的必要条件。
