The interaction between electrons in graphene under high magnetic fields drives the formation of a rich set of quantum Hall ferromagnetic (QHFM) phases with broken spin or valley symmetry. Visualizing atomic-scale electronic wave functions with scanning tunneling spectroscopy (STS), we resolved microscopic signatures of valley ordering in QHFM phases and spectral features of fractional quantum Hall phases of graphene. At charge neutrality, we observed a field-tuned continuous quantum phase transition from a valley-polarized state to an intervalley coherent state, with a Kekulé distortion of its electronic density. Mapping the valley texture extracted from STS measurements of the Kekulé phase, we could visualize valley skyrmion excitations localized near charged defects. Our techniques can be applied to examine valley-ordered phases and their topological excitations in a wide range of materials.

中文翻译：

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可视化量子霍尔铁磁体中的破坏对称性和拓扑缺陷

在高磁场下，石墨烯中电子之间的相互作用驱动了一组丰富的量子霍尔铁磁 (QHFM) 相的形成，这些相具有破碎的自旋或谷对称性。使用扫描隧道光谱 (STS) 可视化原子级电子波函数，我们解决了 QHFM 相中谷序的微观特征和石墨烯分数量子霍尔相的光谱特征。在电荷中性时，我们观察到从谷极化状态到间隔相干状态的场调谐连续量子相变，其电子密度发生 Kekulé 畸变。绘制从 Kekulé 相的 STS 测量中提取的山谷纹理，我们可以看到位于带电缺陷附近的山谷 skyrmion 激发。