New Journal of Physics (Jan 2013)
Doping dependence of the electron–phonon and electron–spin fluctuation interactions in the high-Tc superconductor Bi2Sr2CaCu2O8+δ
Abstract
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+ _δ (Bi-2212) from the underdoped to overdoped regimes. The different doping dependences of the electron–boson coupling strengths enable us to identify them as phonons and spin fluctuations: electron–phonon coupling ( λ _e−ph ) peaks at optimal doping, while electron–spin fluctuation coupling ( λ _e−sf ) decreases monotonically with doping. This observation is consistent with two facts: (i) superconductivity is in close proximity with antiferromagnetism at low dopings and (ii) a pronounced lattice renormalization effect at larger dopings.