Three-dimensional collective charge excitations in electron-doped copper oxide superconductors
Three-dimensional collective charge excitations in electron-doped copper oxide superconductors
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DOI：
10.1038/s41586-018-0648-3
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发表时间：
2018-11-15
期刊：
影响因子：
64.8
通讯作者：
Lee, W. S.
中科院分区：
文献类型：
--
作者：
Hepting, M.;Chaix, L.;Lee, W. S.
高温氧化铜超导体由堆叠的CuO 2平面组成，具有主要是二维的电子能带结构和磁激发（1，2），但具有三维的超导相干性。这种二分法强调了面外电荷动力学的重要性，人们发现，在光学可及的有限动量范围内，面外电荷动力学在正常态（3，4）中是不相干的。在这里，我们使用共振非弹性X射线散射，探索跨越所有三个维度的布里渊区的电荷动力学。最近发现的电子掺杂的铜氧化物（5-7）中的集体激发（模式）的极化分析揭示了它们的电荷来源，也就是说，没有与磁性成分（5-7）混合。激励沿面内和面外两个方向沿着分散，揭示了它的三维性质。面外色散的周期性对应于相邻CuO 2平面之间的距离，而不是晶体学c轴晶格常数，这表明面间库仑相互作用是负责的相干面外电荷动力学。所观察到的性质是长期寻找的“声学等离子体激元”的标志，其是预测用于分层系统的不同电荷集体模式的分支（8-12），并且被认为在介导高温超导性中发挥重要作用（10-12）。
High-temperature copper oxide superconductors consist of stacked CuO2 planes, with electronic band structures and magnetic excitations that are primarily two-dimensional(1,2), but with superconducting coherence that is three-dimensional. This dichotomy highlights the importance of out-of-plane charge dynamics, which has been found to be incoherent in the normal state(3,4) within the limited range of momenta accessible by optics. Here we use resonant inelastic X-ray scattering to explore the charge dynamics across all three dimensions of the Brillouin zone. Polarization analysis of recently discovered collective excitations (modes) in electron-doped copper oxides(5-7) reveals their charge origin, that is, without mixing with magnetic components(5-7). The excitations disperse along both the in-plane and out-of-plane directions, revealing its three-dimensional nature. The periodicity of the out-of-plane dispersion corresponds to the distance between neighbouring CuO2 planes rather than to the crystallographic c-axis lattice constant, suggesting that the interplane Coulomb interaction is responsible for the coherent out-of-plane charge dynamics. The observed properties are hallmarks of the long-sought 'acoustic plasmon, which is a branch of distinct charge collective modes predicted for layered systems(8-12) and argued to play a substantial part in mediating high-temperature superconductivity(10-12).