Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore 117546, Singapore.
Department of Physics, University of California, San Diego, La Jolla, California 92093, USA.
Nat Mater. 2015 Dec;14(12):1217-22. doi: 10.1038/nmat4425. Epub 2015 Sep 28.
Moiré patterns are periodic superlattice structures that appear when two crystals with a minor lattice mismatch are superimposed. A prominent recent example is that of monolayer graphene placed on a crystal of hexagonal boron nitride. As a result of the moiré pattern superlattice created by this stacking, the electronic band structure of graphene is radically altered, acquiring satellite sub-Dirac cones at the superlattice zone boundaries. To probe the dynamical response of the moiré graphene, we use infrared (IR) nano-imaging to explore propagation of surface plasmons, collective oscillations of electrons coupled to IR light. We show that interband transitions associated with the superlattice mini-bands in concert with free electrons in the Dirac bands produce two additive contributions to composite IR plasmons in graphene moiré superstructures. This novel form of collective modes is likely to be generic to other forms of moiré-forming superlattices, including van der Waals heterostructures.
Moiré 图案是当两个晶格略有失配的晶体叠加时出现的周期性超晶格结构。最近一个突出的例子是单层石墨烯放置在六方氮化硼晶体上。由于这种堆叠产生的莫尔超晶格，石墨烯的电子能带结构发生了根本性的改变，在超晶格区边界获得了卫星子狄拉克锥。为了探测莫尔石墨烯的动力学响应，我们使用红外（IR）纳米成像来探索表面等离激元的传播，这是与 IR 光耦合的电子的集体振荡。我们表明，与超晶格 mini-bands 相关的带间跃迁与狄拉克带中的自由电子一起，在石墨烯莫尔超结构中产生了对复合 IR 等离激元的两个附加贡献。这种新形式的集体模式可能是其他形式的莫尔超晶格的通用形式，包括范德华异质结构。
