In conventional superconductors, the interaction that pairs the electrons to form the superconducting state is mediated by lattice vibrations1 (phonons). In high-transition-temperature (high-Tc) copper oxides, it is generally believed that magnetic excitations might play a fundamental role in the superconducting mechanism because superconductivity occurs when mobile ‘electrons’ or ‘holes’ are doped into the antiferromagnetic parent compounds2. Indeed, a sharp magnetic excitation termed ‘resonance’ has been observed by neutron scattering in a number of hole-doped materials3,4,5,6,7,8,9,10,11. The resonance is intimately related to superconductivity12, and its interaction with charged quasi-particles observed by photoemission13,14, optical conductivity15, and tunnelling16 suggests that it might play a part similar to that of phonons in conventional superconductors. The relevance of the resonance to high-Tc superconductivity, however, has been in doubt because so far it has been found only in hole-doped materials17. Here we report the discovery of the resonance in electron-doped superconducting Pr0.88LaCe0.12CuO4-δ (Tc = 24 K). We find that the resonance energy (Er) is proportional to Tc via Er ≈ 5.8kBTc for all high-Tc superconductors irrespective of electron- or hole-doping. Our results demonstrate that the resonance is a fundamental property of the superconducting copper oxides and therefore must be essential in the mechanism of superconductivity.
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We thank E. Dagotto, H. Ding and S. Zhang for discussions. We also thank Y. Ando's group for teaching us how to grow high-quality single crystals of PLCCO. S.D.W. and S.L. are supported by the US National Science Foundation. S.C. is supported by the US DOE Division of Materials Science, Basic Energy Sciences. Oak Ridge National Laboratory is supported by the US DOE through UT/Battelle LLC. SPINS is supported by the US National Science Foundation through the Center for High Resolution Neutron Spectroscopy.
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
This file contains Supplementary Notes and Supplementart Figure 1, showing model calculations for various CEF transitions. Arguments are presented ruling out the possibility of a CEF origin to the magnetic resonance mode we observe, and the CEF excitation influence can be regarded as background scattering underneath the spin fluctuations localized at Q=(0.5, 0.5, 0). (PDF 237 kb)
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Wilson, S., Dai, P., Li, S. et al. Resonance in the electron-doped high-transition-temperature superconductor Pr0.88LaCe0.12CuO4-δ. Nature 442, 59–62 (2006) doi:10.1038/nature04857
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