Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
Phys Rev Lett. 2009 Nov 27;103(22):227201. doi: 10.1103/PhysRevLett.103.227201. Epub 2009 Nov 24.
An outstanding question regarding the probing or possible device applications of correlated electronic materials (CEMs) with layered structure is the extent to which their bulk and surface properties differ or not. The broken translational symmetry at the surface can lead to distinct functionality due to the charge, lattice, orbital, and spin coupling. Here we report on the case of bilayered manganites with hole doping levels corresponding to bulk ferromagnetic order. We find that, although the hole doping level is measured to be the same as in the bulk, the surface layer is not ferromagnetic. Further, our low-energy electron diffraction and x-ray measurements show that there is a c-axis collapse in the outermost layer. Bulk theoretical calculations reveal that, even at fixed doping level, the relaxation of the Jahn-Teller distortion at the surface is consistent with the stabilization of an A-type antiferromagnetic state.
关于具有层状结构的相关电子材料 (CEMs) 的探测或可能的器件应用，一个悬而未决的问题是其体相和表面性质是否存在差异。由于电荷、晶格、轨道和自旋耦合，表面处的平移对称性被破坏会导致明显的功能。在这里，我们报告了具有双层结构的锰氧化物的情况，其空穴掺杂水平对应于体相铁磁有序。我们发现，尽管表面层的空穴掺杂水平与体相相同，但它不是铁磁性的。此外，我们的低能电子衍射和 X 射线测量表明，最外层存在 c 轴坍塌。体相理论计算表明，即使在固定掺杂水平下，表面处 Jahn-Teller 畸变的弛豫也与 A 型反铁磁态的稳定一致。
