Charge Order Lock-in by Electron-Phonon Coupling in La$_{1.675}$Eu$_{0.2}$Sr$_{0.125}$CuO$_4$

TL;DR

This study uses high-resolution RIXS to show that electron-phonon coupling, especially around the charge-order wave vector, plays a key role in stabilizing charge stripes in cuprate superconductors.

Contribution

It provides direct experimental evidence linking electron-phonon coupling enhancement to charge order formation in stripe-ordered cuprates.

Findings

Phonon softening and shorter lifetimes near charge order wave vector.

Electron-phonon coupling increases around the charge-stripe wave vector upon cooling.

Electron-phonon interaction significantly influences charge stripe stability.

Abstract

We report an ultrahigh resolution resonant inelastic x-ray scattering (RIXS) study of the in-plane bond-stretching phonon mode in stripe-ordered cuprate La$_{1.675}$Eu$_{0.2}$Sr$_{0.125}$CuO$_4$. Phonon softening and lifetime shortening are found around the charge ordering wave vector. In addition to these self-energy effects, the electron-phonon coupling is probed by its proportionality to the RIXS cross section. We find an enhancement of the electron-phonon coupling around the charge-stripe ordering wave vector upon cooling into the low-temperature tetragonal structure phase. These results suggest that in addition to electronic correlations, electron-phonon coupling contributes significantly to the emergence of long-range charge-stripe order in cuprates.