Enhanced electron-phonon coupling for charge-density-wave formation in La$_{1.8-x}$Eu$_{0.2}$Sr$_{x}$CuO$_{4+\delta}$

TL;DR

This study reveals that in a cuprate superconductor, electron-phonon coupling is enhanced at the charge density wave wave vector and plays a role in stabilizing the CDW, with implications for understanding high-temperature superconductivity.

Contribution

The paper demonstrates that electron-phonon coupling is enhanced at the CDW wave vector in cuprates and suggests a feedback mechanism stabilizing the CDW, using Cu L3 edge RIXS measurements.

Findings

EPC is enhanced near the CDW wave vector

EPC matrix element decreases with temperature

CDW enhances EPC, which stabilizes the charge order

Abstract

Charge density wave (CDW) correlations are prevalent in all copper-oxide superconductors. While CDWs in conventional metals are driven by coupling between lattice vibrations and electrons, the role of the electron-phonon coupling (EPC) in cuprate CDWs is strongly debated. Using Cu $L_3$ edge resonant inelastic x-ray scattering (RIXS), we study the CDW and Cu-O bond-stretching phonons in the stripe-ordered cuprate La$_{1.8-x}$Eu$_{0.2}$Sr$_{x}$CuO$_{4+\delta}$. We investigate the interplay between charge order and EPC as a function of doping and temperature, and find that the EPC is enhanced in a narrow momentum region around the CDW wave vector. By detuning the incident photon energy from the absorption resonance, we extract an EPC matrix element at the CDW wave vector of $M\simeq$ 0.36 eV, which decreases to $M\simeq$ 0.30 eV at high temperature in the absence of the CDW. Our results suggest a feedback mechanism in which the CDW enhances the EPC which, in turn, further stabilizes the CDW.