菱方石墨烯中涌现电子晶体的实空间可视化
Real-space Visualization of Emergent Electron Crystals in Rhombohedral Graphene
- Cornell University（康奈尔大学）
- National Institute for Materials Science（国立材料研究所）
机构由 AI 辅助整理，请以论文原文为准。
AI总结：
利用扫描隧道显微镜在菱方六层石墨烯中直接观测到从蜂窝到斜方的电子晶体相变，揭示金属性电子晶体及与轨道磁性交织的异常霍尔晶体，确立电子结晶新范式。
AI中文摘要：
强相互作用电子可以自发破缺空间对称性形成电子晶体，维格纳晶体即为典型例子。近期对菱方石墨烯拓扑平带的研究提出了更奇特的结晶形式，包括将电荷序与非平庸拓扑纠缠在一起的异常霍尔晶体，以及局域载流子与巡游载流子共存的金属性电子晶体。然而，这些态的直接实空间观测一直难以实现。本文利用扫描隧道显微镜和扫描隧道谱可视化菱方六层石墨烯中涌现的电子晶体。在低电场和有限空穴掺杂范围内，我们观察到电子晶格图案随空穴密度增加，通过一级量子相变从蜂窝状演化为斜方序。从准粒子干涉测量提取的费米面缺乏通过传统嵌套解释这些图案所需的几何结构。结合金属输运和远低于掺杂载流子密度的晶体位点密度，这支持了金属性电子晶体，其中部分载流子结晶。蜂窝状晶体占据与先前输运中观察到的多铁性轨道磁性相同的相空间，并表现出小磁场下的畴稳定效应，这可能暗示一种可能的金属性异常霍尔晶体。随着磁场增加，斜方相发展出$\sqrt{2}\times\sqrt{2}$重构，晶体子格能量劈裂随磁场线性增加，对应$g$因子为16。这可能反映了一种轨道反铁磁电子晶体，其轨道磁化在晶格上交替排列。这些结果确立了电子结晶的新范式，其中电荷序与轨道磁性相互交织。
英文摘要：
Strongly interacting electrons can spontaneously break spatial symmetries to form electron crystals, exemplified by the Wigner crystal. Recent studies of topological flat bands in rhombohedral graphene have suggested more exotic forms of crystallization, including anomalous Hall crystals that entangle charge order with nontrivial topology and metallic electron crystals in which localized and itinerant carriers coexist. Direct real-space observation of these states, however, has remained elusive. Here we use scanning tunneling microscopy and spectroscopy to visualize emergent electron crystals in rhombohedral hexalayer graphene. At low electric fields and over a finite range of hole doping, we observe electronic lattice patterns that evolve from honeycomb to oblique order through a first-order quantum phase transition with increasing hole density. The Fermi surface extracted from quasiparticle-interference measurements lacks the geometry needed to account for these patterns through conventional nesting. Together with metallic transport and a crystal-site density much lower than the doped carrier density, this supports metallic electron crystals in which a subset of carriers crystallizes. The honeycomb crystal occupies the same phase space as the multiferroic orbital magnetism observed previously in transport and exhibits domain stabilization by a small magnetic field, which may suggest a possible metallic anomalous Hall crystal. With increasing magnetic field, the oblique phase develops a $\sqrt{2}\times\sqrt{2}$ reconstruction with a crystal-sublattice energy splitting that increases linearly with field, corresponding to a $g$-factor of 16. This may reflect an orbital-antiferromagnetic electron crystal with alternating orbital magnetization across the lattice. These results establish a new paradigm of electron crystallization in which charge order is intertwined with orbital magnetism.
