Elbert E. M. Chia, D. Springer, Saritha K. Nair, X. Q. Zou, S. A. Cheong, C. Panagopoulos, T. Tamegai, H. Eisaki, S. Ishida, S. Uchida, A. J. Taylor, Jian-Xin Zhu
Using ultrafast optical techniques, we detect two types of bosons strongly coupled to electrons in the family of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ from the underdoped to overdoped regimes. The different doping dependences of the electron-boson coupling strengths enables us to identify them as phonons and spin fluctuations: electron-phonon coupling ($\lambda_{e-ph}$) peaks at optimal doping, and electron-spin fluctuation coupling ($\lambda_{e-sf}$) decreases monotonically with doping. This observation is consistent with two facts: (1) superconductivity is in close proximity with antiferromagnetism at low dopings, and (2) a pronounced lattice renormalization effect at larger dopings.
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http://arxiv.org/abs/1107.1924
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