Type: Article
Publication Date: 2008-06-04
Citations: 77
DOI: https://doi.org/10.1103/physrevlett.100.227002
We report the first measurement of the Cu-O bond stretching phonon dispersion in optimally doped ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{1.6}{\mathrm{La}}_{0.4}{\mathrm{Cu}}_{2}{\mathrm{O}}_{6+\ensuremath{\delta}}$ using inelastic x-ray scattering. We found a softening of this phonon at $\mathbf{q}=(\ensuremath{\approx}0.25,0,0)$ from 76 to 60 meV, similar to the one reported in other cuprates. A comparison with angle-resolved photoemission data on the same sample revealed an excellent agreement in terms of energy and momentum between the angle-resolved photoemission nodal kink and the soft part of the bond stretching phonon. Indeed, we find that the momentum space where a $63\ifmmode\pm\else\textpm\fi{}5\text{ }\text{ }\mathrm{meV}$ kink is observed can be connected with a vector $\mathbf{q}=(\ensuremath{\xi},0,0)$ with $\ensuremath{\xi}\ensuremath{\ge}0.22$, corresponding exactly to the soft part of the bond stretching phonon.