Theoretical Quantum Physics Laboratory, RIKEN Cluster for Pioneering Research, Wako-shi, Saitama 351-0198, Japan.
Institute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences, Moscow, 125412 Russia.
Phys Rev Lett. 2018 Jun 29;120(26):266402. doi: 10.1103/PhysRevLett.120.266402.
We theoretically study the effects of electron-electron interaction in twisted bilayer graphene in a transverse dc electric field. When the twist angle is not very small, the electronic spectrum of the bilayer consists of four Dirac cones inherited from each graphene layer. An applied bias voltage leads to the appearance of two holelike and two electronlike Fermi surface sheets with perfect nesting among electron and hole components. Such a band structure is unstable with respect to the exciton band-gap opening due to the screened Coulomb interaction. The exciton order parameter is accompanied by spin-density-wave order. The gap depends on the twist angle and can be varied by a bias voltage. This result correlates well with recent transport measurements [J.-B. Liu et al., Sci. Rep. 5, 15285 (2015)SRCEC32045-232210.1038/srep15285]. Our proposal allows the coexistence of (i) an externally controlled semiconducting gap and (ii) a nontrivial multicomponent magnetic order. This is interesting for both fundamental research and applications.
我们从理论上研究了在横向直流电场中扭曲双层石墨烯中电子-电子相互作用的影响。当扭转角不是非常小时，双层的电子谱由每个石墨烯层继承的四个狄拉克锥组成。外加偏压会导致出现两个空穴型和两个电子型费米表面片，其中电子和空穴分量之间具有完美的嵌套。由于屏蔽库仑相互作用，这种带结构对于激子带隙打开是不稳定的。激子有序参量伴随着自旋密度波有序。间隙取决于扭转角并且可以通过偏压来改变。这一结果与最近的输运测量结果[J.-B. Liu 等人，Sci. Rep. 5, 15285 (2015)SRCEC32045-232210.1038/srep15285]很好地相关。我们的方案允许（i）外部控制的半导体间隙和（ii）非平凡的多分量磁有序共存。这对于基础研究和应用都很有趣。
