ARPES Spectra of Bi2212 give the Coulomb Coupling $\lambda ^{C}\approx 1$ and the Electron-Phonon Coupling $\lambda ^{EP}=2-3$

Abstract

We show that the double kink-structure in the electronic self-energy of Bi2212 near the nodal point at low energy $\omega_{1}\approx 50-70$ $meV$ and at high energy at $\omega_{2}\approx 350$ $meV$, observed recently in the ARPES measurements by Valla et al \cite{Valla-2006}, gives that the electron-phonon (EPI) coupling constant $\lambda_{z}^{EP}$in the normal part of the self-energy $\Sigma (\omega)$ is twice larger than the Coulomb coupling $\lambda_{z}^{C}$. The experimental data for $\func{Re}\Sigma (\omega)$ up to energies $\sim 350$ $meV$ can be satisfactory explained by $% \lambda_{z}^{EP}\approx 2.1$ and $\lambda_{z}^{C}\approx 1.1$. Additionally the low energy slope of the ARPES $\func{Re}\Sigma (\omega)$ at $\omega <20$ $meV$ \cite{Valla-2006} gives a hint that the low energy phonons might contribute significantly to the EPI coupling, i.e. $\lambda_{z}^{low,EP}>1$, thus giving the total EPI coupling constant $\lambda_{z,tot}^{EP}=\lambda_{z}^{EP}+\lambda_{z}^{low,EP}>3$. In order to test the role of low frequency phonons by ARPES measurements a much better momentum resolution is needed than that reported in \cite{Valla-2006}. Possible pairing scenarios based on ARPES, tunnelling and magnetic neutron scattering measurements are discussed.