Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Department of Physics and Astronomy, California State University, Northridge, California 91330, USA.
Phys Rev Lett. 2019 Aug 23;123(8):087602. doi: 10.1103/PhysRevLett.123.087602.
Inspired by the recent discovery of correlated insulating states in twisted bilayer graphene, we study a two-orbital Hubbard model on the honeycomb lattice with two electrons per unit cell. Based on the real-space density matrix renormalization group simulation, we identify a metal-insulator transition around U_{c}/t=2.5-3. In the vicinity of U_{c}, we find strong spin-orbital density wave fluctuations at commensurate wave vectors, accompanied by weaker incommensurate charge density wave fluctuations. The spin-orbital density wave fluctuations are enhanced with increasing system sizes, suggesting the possible emergence of long-range order in the two-dimensional limit. At larger U, our calculations indicate a possible nonmagnetic Mott insulator phase without spin or orbital polarization. Our findings offer new insight into correlated electron phenomena in twisted bilayer graphene and other multiorbital honeycomb materials.
受扭曲双层石墨烯中关联绝缘态的最新发现启发，我们研究了一个每个单元包含两个电子的双轨道 Hubbard 模型在蜂窝晶格上的情况。基于实空间密度矩阵重整化群模拟，我们确定了在 U_{c}/t=2.5-3 附近的金属-绝缘相变。在 U_{c}附近，我们发现了在合频波矢处具有强自旋轨道密度波涨落，伴随着较弱的非合频电荷密度波涨落。自旋轨道密度波涨落随着系统尺寸的增加而增强，这表明在二维极限下可能出现长程有序。在更大的 U 下，我们的计算表明可能存在没有自旋或轨道极化的非磁性莫特绝缘相。我们的发现为扭曲双层石墨烯和其他多轨道蜂窝材料中的关联电子现象提供了新的见解。
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