Angle-resolved photoemission spectra of ${\mathrm{Bi}}_2{\mathrm{Sr}}_2\mathrm{Ca}{\mathrm{Cu}}_2{\mathrm{O}}_8$ show a Coulomb coupling $\approx 1$ and an electron-phonon coupling of $2-3$

We show that the double kink structure in the electronic self-energy of Bi2212 near the nodal point at low energy ${\omega }_1\approx 50–70\mathrm{meV}$ and at high energy at ${\omega }_2\approx 0.35–0.4\mathrm{eV}$, observed recently in the angle-resolved photoemission spectra (ARPES) measurements can be explained by the electron-phonon interaction (EPI) coupling constant [in the normal part of the self-energy $\mathrm{Re}\Sigma \left(\omega \right)$] ${\lambda }_z^{EP}\approx 2.1$ and the Coulomb coupling ${\lambda }_z^C\approx 1.1$. Additionally, the low-energy slope of the ARPES $\mathrm{Re}\Sigma \left(\omega \right)$ at $\omega <20\mathrm{meV}$ by Valla et al. gives a hint that low-energy phonons might contribute significantly to the EPI coupling, i.e., ${\lambda }_z^{\mathit{\text{low}},EP}>1$, thus giving the total EPI coupling constant ${\lambda }_{z,\mathit{tot}}^{EP}={\lambda }_z^{EP}+{\lambda }_z^{\mathit{\text{low}},EP}>3$. In order to test the role of low-energy phonons by ARPES measurements much better momentum resolution is needed than that reported by Valla et al. Possible pairing scenarios based on ARPES, tunneling, and magnetic neutron scattering measurements are discussed.

Figure 1

(Color online) Figure 4(b) from Ref. 18: $\mathrm{Re}\Sigma \left(\omega \right)$ measured in Bi2212 (thin line) and model $\mathrm{Re}\Sigma \left(\omega \right)$ (bold line) obtained in Ref. 18. The three thin lines $({\lambda }_1,{\lambda }_2,{\lambda }_3)$ are the slopes of $\mathrm{Re}\Sigma \left(\omega \right)$ in different energy regions.