Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, USA.
Nat Mater. 2014 Jun;13(6):586-92. doi: 10.1038/nmat3964. Epub 2014 May 18.
The cooperative Jahn-Teller effect (CJTE) refers to the correlation of distortions arising from individual Jahn-Teller centres in complex compounds. The effect usually induces strong coupling between the static or dynamic charge, orbital and magnetic ordering, which has been related to many important phenomena such as colossal magnetoresistance and superconductivity. Here we report a Na5/8MnO2 superstructure with a pronounced static CJTE that is coupled to an unusual Na vacancy ordering. We visualize this coupled distortion and Na ordering down to the atomic scale. The Mn planes are periodically distorted by a charge modulation on the Mn stripes, which in turn drives an unusually large displacement of some Na ions through long-ranged Na-O-Mn(3+)-O-Na interactions into a highly distorted octahedral site. At lower temperatures, magnetic order appears, in which Mn atomic stripes with different magnetic couplings are interwoven with each other. Our work demonstrates the strong interaction between alkali ordering, displacement, and electronic and magnetic structure, and underlines the important role that structural details play in determining electronic behaviour.
协同 Jahn-Teller 效应 (CJTE) 是指复杂化合物中单个 Jahn-Teller 中心引起的畸变之间的相关性。该效应通常会导致静态或动态电荷、轨道和磁有序之间的强烈耦合，这与许多重要现象有关，如巨磁电阻和超导性。在这里，我们报告了一种具有明显静态 CJTE 的 Na5/8MnO2 超结构，该超结构与不寻常的 Na 空位有序相关联。我们在原子尺度上可视化了这种耦合的畸变和 Na 有序。Mn 平面通过 Mn 条纹上的电荷调制周期性地变形，这反过来又通过长程 Na-O-Mn(3+)-O-Na 相互作用驱动一些 Na 离子异常大的位移，进入高度扭曲的八面体位置。在较低温度下，出现了磁有序，其中具有不同磁耦合的 Mn 原子条纹相互交织在一起。我们的工作证明了碱金属有序、位移以及电子和磁结构之间的强烈相互作用，并强调了结构细节在决定电子行为方面的重要作用。
