论文标题
扭曲的双层石墨烯中的平流型铁磁性
Flat-band ferromagnetism in twisted bilayer graphene
论文作者
论文摘要
我们讨论了基于Mielke和Tasaki提出的平坦带铁磁性定理的扭曲双层石墨烯（TBG）。根据该定理，如果平面频段状态的单个粒子密度矩阵不可还原，我们认为可以将此结果应用于TBG的准芬特频段，而tbg的准平线频段围绕电荷 - 中性型的旋转角度出现，则可以将此结果应用于魔法角度$θ\ sim1.055^\ $ $。我们表明，在这种情况下，密度矩阵不可修复，从而预测了中性TBG的铁磁基态（$ n = 0 $）。然后，如果基板在电荷中立诱导单粒子间隙，我们也可以证明定理也只能应用于平坦传导或价带。同样在这种情况下，相应的密度矩阵证明是不可约的，导致一半填充时的铁磁（$ n = \ pm2 $）。
We discuss twisted bilayer graphene (TBG) based on a theorem of flat band ferromagnetism put forward by Mielke and Tasaki. According to this theorem, ferromagnetism occurs if the single particle density matrix of the flat band states is irreducible and we argue that this result can be applied to the quasi-flat bands of TBG that emerge around the charge-neutrality point for twist angles around the magic angle $θ\sim1.05^\circ$. We show that the density matrix is irreducible in this case, thus predicting a ferromagnetic ground state for neutral TBG ($n=0$). We then show that the theorem can also be applied only to the flat conduction or valence bands, if the substrate induces a single-particle gap at charge neutrality. Also in this case, the corresponding density matrix turns out to be irreducible, leading to ferromagnetism at half filling ($n=\pm2$).
