二维联苯网络的磁有序、反常Lifshitz相变和拓扑晶界
Magnetic Ordering, Anomalous Lifshitz Transition and Topological Grain Boundaries in Two-Dimensional Biphenylene Network
摘要：
研究了一种由联苯分子网络化形成的平面碳晶体的电子性质。碳材料中的新的电子特征，如带中心鞍点和特殊的II型狄拉克费米子态被证明存在于低能电子谱。这里的II型状态有一个几乎平坦的分支，并且接近于向I型的过渡。讨论了可能与低能带有关的磁不稳定性。此外，在适度的单轴应变下，一对狄拉克点与区域中心鞍点合并，实现了范霍夫奇点的Lifshitz跃迁和狄拉克费米子的对湮灭。一个新的有效的哈密顿量，包括所有独特的低能量状态的构建，揭示了一个有限的缠绕数的伪自旋纹理周围的狄拉克点，量子化Zak阶段，和拓扑晶界状态。
英文摘要：
We study electronic properties of a new planar carbon crystal formed through networking biphenylene molecules. Novel electronic features among carbon materials such as zone-center saddle point and peculiar type-II Dirac fermionic states are shown to exist in the low energy electronic spectrum. The type-II state here has a nearly flat branch and is close to a transition to type-I. Possible magnetic instabilities related with low energy bands are discussed. Furthermore, with a moderate uniaxial strain, a pair of Dirac points merge with the zone center saddle point, realizing concurrent Lifshitz transitions of van Hove singularity as well as pair annihilation of the Dirac fermions. A new effective Hamiltonian encompassing all distinctive low energy states is constructed, revealing a finite winding number of the pseudo-spin texture around the Dirac point, quantized Zak phases, and topological grain boundary states.
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