石墨烯莫尔超晶格

石墨烯莫尔超晶格来源于六方氮化硼衬底对石墨烯的二维周期势调控. 由于这种外加的周期势对石墨烯能带具有显著的调制作用, 近年来引发了人们广泛的关注. 利用氮化硼衬底上外延的单晶石墨烯薄膜, 我们系统研究了基底调制下的莫尔超晶格以及相关的物理特性. 首先, 我们在电子端和空穴端都观测到了超晶格狄拉克点, 并且超晶格狄拉克点同本征狄拉克点类似, 都表现出绝缘体的特性. 在低温强磁场下, 可以观测到到单层石墨烯和双层石墨烯的量子霍尔效应. 并且, 从朗道扇形图中, 可以清晰的看到磁场下形成的超晶格朗道能级. 此外, 利用红外光谱的方法研究了强磁场下石墨烯超晶格体系不同朗道能级之间的跃迁, 发现这种跃迁满足有质量狄拉克费米子的行为, 对应38 meV的本征能隙. 在此基础上, 我们在380 meV位置发现一个同超晶格能量对应的光电导峰. 通过利用旋量势中三个不同的势分量对光电导峰进行拟合, 发现赝自旋杂化势起主导作用. 进一步研究表明赝自旋杂化势强度随载流子浓度的增大显著降低, 表明电子-电子相互作用引起的旋量势的重构.

Graphene/h-BN Moiré superlattice

Graphene Moiré superlattice, a unique 2D periodical structure originated from the interaction between graphene and its supporting substrate h-BN, has attracted great interest recently. Employing epitaxial graphene on h-BN single crystals, we have investigated systematically the physical properties related to the Moiré superlattice. From transport measurements, we can observe the superlattice Dirac points at both electron side and hole side. Similar to the Dirac point, the superlattice Dirac points have insulator behaviors. Under the action of magnetic field, the quantum Hall effects both in monolayer and bilayer graphenes are observed. Also, the Moiré superlattice can lead to the formation of self-similar mini-bands from the Landau fan diagram. According to the infrared optical spectroscopy measurements, the transitions between different Landau levels are characterized by massive Dirac fermions and thus reveal a band-gap of ～38 meV. Moreover, without magnetic fields, an optical conductivity peak related to the Moiré superlattice appears. We use three spinor potential components to explain the optical conductivity peak and demonstrate that the pseudospin-mixing component plays a dominant role in the spinor potential. In addition, the spinor potential depends sensitively on the gate voltage, indicating that the electron–electron interactions play an important part in the renormalization of the spinor potential.