  Since conventional superconductivity is mediated by phonons, their role in
the mechanism of high temperature superconductivity has been considered very
early after the discovery of the cuprates. The initial consensus was that
phonons could not produce transition temperatures near 100K, and the main
direction of research focused on nonphononic mechanisms. Subsequent work last
reviewed by L. Pintschovius in 2005 showed that electron-phonon coupling in the
cuprates is surprisingly strong for some phonons and its role is controversial.
Experiments performed since then identified anomalous behavior of certain Cu-O
bond-stretching phonons in cuprates as an important phenomenon that is somehow
related to the mechanism of superconductivity. A particularly big advance was
made in the study of doped La2CuO4. This work is reviewed here.
