Characteristics of oxygen isotope substitutions in the quasiparticle spectrum of Bi₂Sr₂CaCu₂O₈₊

¹  Institute of Theoretical and Computational Physics, Graz University of Technology - A-8010 Graz, Austria, EU
²  Department of Physics and Astronomy, McMaster University - Hamilton, Ontario N1G 2W1, Canada
³  The Canadian Institute for Advanced Research - Toronto, Ontario M5G 1Z8, Canada

Corresponding author: Schachinger@itp.tu-graz.ac.at

Received: 30 April 2009
Accepted: 9 June 2009

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 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 Bi₂Sr₂CaCu₂O₈₊ phonons contribute ~ 10% and non-phononic excitations ~ 90%.