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Pressure-induced gap modulation and topological transitions in twisted bilayer and twisted double bilayer graphene

机译：扭曲双层和扭曲双双层石墨烯的压力诱导的间隙调制和拓扑过渡

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摘要

We study the electronic and topological properties of fully relaxed twisted bilayer (TBG) and twisted double bilayer (TDBG) graphene under perpendicular pressure. An approach has been proposed to obtain the equilibrium in-plane structural deformation and out-of-plane corrugation in moire superlattices under pressure. We find that the in-plane relaxation becomes much stronger under higher pressure, while the corrugation height in each layer is maintained. A comparison between the band structures of relaxed and rigid structures demonstrates that not only the gaps on the electron and hole sides (Δ_e and Δ_h) are significantly underestimated without relaxation, but also the detailed dispersions of the middle bands of rigid structures are rather different from those of relaxed systems. Δ_e and Δ_h in TBG reach maximum values around critical pressures with the narrowest middle bands. Topological transitions occur in TDBG under pressure with the middle valence and conduction bands in one valley touching and their Chern numbers transferred to each other. The pressure can also tune the gap at the neutrality point of TDBG. which becomes closed for a pressure range and reopened under higher pressure. The behavior of the electronic structure of superlattices under pressure is sensitive to the twist angle θ with the critical pressures generally increasing with θ.
机译：我们在垂直压力下研究完全松弛的双层双层（TBG）和扭曲双双层（TDBG）石墨烯的电子和拓扑特性。已经提出了一种方法来在压力下获得Moire超晶格中的平平面结构变形和平面外波纹。我们发现，在较高压力下，面内弛豫变得更强烈，而每层的波纹高度保持在较高的压力下。宽松和刚性结构的带结构之间的比较表明，不仅在没有松弛而不弛豫的情况下显着低估了电子和孔侧（Δ_e和Δ_h）上的间隙，而且刚性结构的中间带的详细分散器与那些放松的系统。 TBG中的Δ_e和Δ_h达到临界压力周围的最大值，具有最窄的中间带。拓扑过渡在TDBG下发生在压力下，其中一个谷触摸的中间价和导电带，并且它们的挖掘号彼此传输。压力还可以调节TDBG中性点处的间隙。这对于压力范围关闭并在更高的压力下重新开放。在压力下超晶格的电子结构的行为对扭转角θ敏感，临界压力通常随θ增加。

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  • 来源
    《Physical review》 |2020年第15期|155405.1-155405.10|共10页
  • 作者

    Xianqing Lin; Haotian Zhu; Jun Ni;

  • 作者单位

    College of Science Zhejiang University of Technology Hangzhou 310023 People's Republic of China;

    College of Science Zhejiang University of Technology Hangzhou 310023 People's Republic of China;

    State Key Laboratory of Low-Dimensional Quantum Physics and Frontier Science Center for Quantum Information Department of Physics Tsinghua University Beijing 100084 People's Republic of China;

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