标题： 超薄RuO$_2$的莫尔辅助电荷不稳定性 显示英文标题

标题： Moiré-assisted charge instability in ultrathin RuO$_2$

摘要： 二氧化钌（RuO$_2$）已成为当代凝聚态物理研究的焦点，作为反铁磁性的典型候选材料。 面对尽管有理论预测但仍有令人困惑的体磁序证据，自然会将研究重点放在薄膜上，其中库仑相互作用在维度上被抑制，可能产生更强烈的关联环境，容易发生磁序。 在这里，我们结合扫描隧道显微镜（STM）、密度泛函理论（DFT）和密度矩阵重正化群（DMRG）方法，研究在Ru(0001)上生长的原子有序超薄RuO$_2$（110）层。 与磁序的预测相反，我们观察到一种非磁性的电荷密度波（CDW）不稳定性，这是由平坦能带表面态内的费米面嵌套驱动的，并通过与基底的非公度莫尔堆叠稳定。 我们进一步识别出一种非磁性和亚稳的2$\times$ 2表面重构，它破坏了面内镜像对称性，并可通过STM探针操作可逆地切换。 我们的自旋极化STM测量在RuO$_2$表面未发现任何磁不稳定的迹象。 尽管我们的发现否定了关于RuO$_2$体或表面磁性的各种提议，但我们确立了超薄RuO$_2$（110）作为一个有趣的平台，用于探索莫尔辅助的电子表面有序。 显示英文摘要

摘要： Ruthenium dioxide (RuO$_2$) has been in the focus of contemporary condensed matter research as a prototypical candidate material for altermagnetism. In the face of daunting evidence for bulk magnetic order despite promising theoretical predictions, it naturally suggests the focus on thin films where Coulomb interactions are dimensionally quenched and may yield a more strongly correlated environment prone to magnetic ordering. Here, we combine scanning tunneling microscopy (STM), density functional theory (DFT), and density matrix renormalization group (DMRG) methods to investigate atomically ordered ultrathin RuO$_2$(110) grown on Ru(0001). Contrary to predictions of magnetic order, we observe a nonmagnetic charge density wave (CDW) instability that is driven by Fermi surface nesting within the flat-band surface state, and stabilized by the incommensurate moir\'e stacking with the substrate. We further identify a nonmagnetic and metastable 2 $\times$ 2 surface reconstruction that breaks in-plane mirror symmetry and can be reversibly toggled via STM tip manipulation. Our spin-polarized STM measurements find no sign of any magnetic instability at the RuO$_2$ surface. As much as our findings refute proposals for either bulk or surface magnetism in RuO$_2$, we establish ultrathin RuO$_2$(110) as an intriguing platform for exploring Moir\'e-assisted electronic surface order.