arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2008.06441cond-mat.mes-hall
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磁包覆扭曲双层石墨烯中的自发谷螺旋

Spontaneous Valley Spirals in Magnetically Encapsulated Twisted Bilayer Graphene

Tobias M. R. Wolf, Oded Zilberberg, Gianni Blatter, Jose L. Lado

摘要:

范德华异质结构提供了一个丰富的平台,涌现物理由于其可调的杂化电子轨道和自旋自由度。在这里,我们表明,由扭曲的双层石墨烯夹在铁磁绝缘体之间形成的异质结构发展的平带源于扭曲,交换接近和自旋轨道耦合之间的相互作用。我们证明,在这个平带制度,自旋自由度是杂化的,从而产生一个有效的三角形超晶格谷作为一个退化的赝自旋自由度。半填充时的电子相互作用的减弱导致自发的谷混合态,即,谷扇区中的相关状态与谷旋量的几何挫折。我们发现,电层间偏置产生的有效模型中的人工谷轨道耦合,控制谷各向异性和相关态的微观细节,这两种现象理解的谷-海森堡模型与易平面各向异性交换。我们的研究结果提出了扭曲的石墨烯之间的磁性范德华异质结构作为平台,探索纯粹的谷相关态的石墨烯。

英文摘要:

Van der Waals heterostructures provide a rich platform for emergent physics due to their tunable hybridization of electronic orbital- and spin-degrees of freedom. Here, we show that a heterostructure formed by twisted bilayer graphene sandwiched between ferromagnetic insulators develops flat bands stemming from the interplay between twist, exchange proximity and spin-orbit coupling. We demonstrate that in this flat-band regime, the spin degree of freedom is hybridized, giving rise to an effective triangular superlattice with valley as a degenerate pseudospin degree of freedom. Incorporating electronic interactions at half-filling leads to a spontaneous valley-mixed state, i.e., a correlated state in the valley sector with geometric frustration of the valley spinor. We show that an electric interlayer bias generates an artificial valley-orbit coupling in the effective model, controlling both the valley anisotropy and the microscopic details of the correlated state, with both phenomena understood in terms of a valley-Heisenberg model with easy-plane anisotropic exchange. Our results put forward twisted graphene encapsulated between magnetic van der Waals heterostructures as platforms to explore purely valley-correlated states in graphene.

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