C. Gadermaier, V. V. Kabanov, A. S. Alexandrov, L. Stojchevska, T. Mertelj, C. Manzoni, G. Cerullo, N. D. Zhigadlo, J. Karpinski, Y. Q. Cai, X. Yao, Y. Toda, M. Oda, S. Sugai, D. Mihailovic
The pairing mechanism at the origin of high-temperature superconductivity is still the subject of passionate debate. Ample experimental evidence suggests that in high-temperature superconductors the electrons interact strongly with two types of collective (bosonic) excitations: lattice vibrations (phonons), and collective electronic excitations, such as spin fluctuations. However, evidence for strong interaction is not sufficient to identify the pairing mechanism. Here we show that the superconducting critical temperature Tc of pnictides, cuprates, and bismuthates depends universally on the strength of the electron-phonon interaction as measured by the electron energy relaxation rate, showing a characteristic maximum at ~ 15 ps-1, Tc > 130 K. This dependence demonstrates that the electron-phonon interaction is fundamental for the pairing. Among the many scenarios that have been proposed for the high-Tc mechanism, we find that only bipolaronic pairing is consistent with the experimental results.
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http://arxiv.org/abs/1205.4978
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