期刊
NATURE
卷 563, 期 7731, 页码 374-+出版社
NATURE PUBLISHING GROUP
DOI: 10.1038/s41586-018-0648-3
关键词
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资金
- US Department of Energy (DOE), Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division [DE-AC02-76SF00515]
- Department of Energy, SLAC Laboratory Directed Research and Development [DE-AC02-76SF00515]
- ERC-P-ReXS project of the Fondazione CARIPLO [2016-0790]
- Regione Lombardia, in Italy
- NSF [DMR-1708334]
- US DOE [DE-AC02-05CH11231]
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).
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