El Baggari Ismail, Baek David J, Zachman Michael J, Lu Di, Hikita Yasuyuki, Hwang Harold Y, Nowadnick Elizabeth A, Kourkoutis Lena F
Department of Physics, Cornell University, Ithaca, NY, USA.
School of Electrical and Computer Engineering, Cornell University, Ithaca, NY, USA.
Nat Commun. 2021 Jun 18;12(1):3747. doi: 10.1038/s41467-021-24026-7.
The self-organization of strongly interacting electrons into superlattice structures underlies the properties of many quantum materials. How these electrons arrange within the superlattice dictates what symmetries are broken and what ground states are stabilized. Here we show that cryogenic scanning transmission electron microscopy (cryo-STEM) enables direct mapping of local symmetries and order at the intra-unit-cell level in the model charge-ordered system NdSrMnO. In addition to imaging the prototypical site-centered charge order, we discover the nanoscale coexistence of an exotic intermediate state which mixes site and bond order and breaks inversion symmetry. We further show that nonlinear coupling of distinct lattice modes controls the selection between competing ground states. The results demonstrate the importance of lattice coupling for understanding and manipulating the character of electronic self-organization and that cryo-STEM can reveal local order in strongly correlated systems at the atomic scale.
强相互作用电子自组织形成超晶格结构是许多量子材料性质的基础。这些电子在超晶格中的排列方式决定了哪些对称性被打破以及哪些基态得以稳定。在此，我们表明低温扫描透射电子显微镜（cryo-STEM）能够直接绘制出模型电荷有序体系NdSrMnO中晶胞内局部对称性和有序性的图谱。除了对典型的以位点为中心的电荷有序进行成像外，我们还发现了一种奇异中间态的纳米尺度共存，该中间态混合了位点和键序并打破了反演对称性。我们进一步表明，不同晶格模式的非线性耦合控制着竞争基态之间的选择。这些结果证明了晶格耦合对于理解和操控电子自组织特性的重要性，并且cryo-STEM能够在原子尺度上揭示强关联体系中的局部有序性。
