论文标题
扭曲双层石墨烯中的应变诱导的兴奋子不稳定性
Strain-induced excitonic instability in twisted bilayer graphene
论文作者
论文摘要
扭曲的双层石墨烯的低能带形成了零孔，在小旋转角度上具有近似的电子孔对称性。这些杂交受到Moiré模式的新兴对称性的保护，并赋予了谱带拓扑特征。在层之间积累的应变（异形）在能量和动量方面都会移动狄拉克点。传导和价带的重叠有利于靠近中性点的费米表面的激素不稳定性。电子孔对的自发凝结破坏了时间逆转对称性和每个山谷部门内电荷的单独保护。该顺序参数描述了层间循环电流，这些电流在kekulé样轨道磁化密度波中。由于频带的基础拓扑，该顺序参数中的涡流携带费用数字。这种机制可能解释了最均匀样品中中立性绝缘状态的发生，在最均匀的样品中，均匀应变场既有助于稳定层之间的相对方向，又有助于兴奋子间隙之间的相对方向。
The low-energy bands of twisted bilayer graphene form Dirac cones with approximate electron-hole symmetry at small rotation angles. These crossings are protected by the emergent symmetries of moiré patterns, conferring a topological character to the bands. Strain accumulated between layers (heterostrain) shifts the Dirac points both in energy and momentum. The overlap of conduction and valence bands favors an excitonic instability of the Fermi surface close to the neutrality point. The spontaneous condensation of electron-hole pairs breaks time reversal symmetry and the separate conservation of charge within each valley sector. The order parameter describes interlayer circulating currents in a Kekulé-like orbital magnetization density wave. Vortices in this order parameter carry fermion numbers owing to the underlying topology of the bands. This mechanism may explain the occurrence of insulating states at neutrality in the most homogenous samples, where uniform strain fields contribute both to stabilizing the relative orientation between layers and to the formation of an excitonic gap.
