# Characteristics of oxygen isotope substitutions in the quasiparticle spectrum of Bi 2 Sr 2 CaCu 2 O 8+δ Academic Article

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### abstract

• There is an ongoing debate about the nature of the bosonic excitations responsible for the quasiparticle self energy in high temperature superconductors -- are they phonons or spin fluctuations? We present a careful analysis of the bosonic excitations as revealed by the `kink' feature at 70 meV in angle resolved photoemission data using Eliashberg theory for a d-wave superconductor. Starting from the assumption that nodal quasiparticles are not coupled to the $(\pi,\pi)$ magnetic resonance, the sharp structure at $70$meV can be assigned to phonons. We find that not only can we account for the shifts of the kink energy seen on oxygen isotope substitution but also get a quantitative estimate of the fraction of the area under the electron-boson spectral density which is due to phonons. We conclude that for optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ phonons contribute $\sim 10$% and non-phononic excitations $\sim 90$%.

• June 1, 2009