Bond stretching phonon softening and angle-resolved photoemission kinks in optimally doped Bi2Sr1.6La0.4Cu2O6 superconductors

TL;DR

This study measures phonon dispersion in optimally doped Bi2Sr1.6La0.4Cu2O6 superconductors and finds a strong correlation between phonon softening and ARPES kinks, supporting electron-phonon coupling as a key factor.

Contribution

First direct measurement of optical phonon dispersion in this superconductor showing phonon softening linked to ARPES kinks, indicating electron-phonon interaction.

Findings

Phonon softening observed at q=(0.25,0,0) from 76 to 60 meV.

Excellent energy and momentum agreement between ARPES kinks and phonon modes.

Kink momentum vector matches the soft phonon mode vector.

Abstract

We report the first measurement of the optical phonon dispersion in optimally doped single layer Bi2Sr1.6La0.4Cu2O6+delta using inelastic x-ray scattering. We found a strong softening of the Cu-O bond stretching phonon at about q=(0.25,0,0) from 76 to 60 meV, similar to the one reported in other cuprates. A direct comparison with angle-resolved photoemission spectroscopy measurements taken on the same sample, revealed an excellent agreement in terms of energy and momentum between the ARPES nodal kink and the soft part of the bond stretching phonon. Indeed, we find that the momentum space where a 63 meV kink is observed can be connected with a vector q=(xi,0,0) with xi~0.22, which corresponds exactly to the soft part of the bond stretching phonon mode. This result supports an interpretation of the ARPES kink in terms of electron-phonon coupling.