Electron-phonon interaction in n-doped cuprates: an Inelastic X-ray Scattering study

TL;DR

This study uses high-resolution inelastic x-ray scattering to measure phonon dispersion in electron-doped cuprates, revealing softening effects indicative of strong electron-phonon coupling relevant to high-temperature superconductivity.

Contribution

It demonstrates the effectiveness of IXS in probing phonon behavior in small samples and uncovers specific phonon softening linked to electron doping in cuprates.

Findings

Two LO phonon branches shift to lower energies with doping

Anomalous phonon softening observed around q=(0.2,0,0)

Evidence of strong electron-phonon coupling in electron-doped cuprates

Abstract

Inelastic x-ray scattering (IXS) with very high (meV) energy resolution has become a valuable spectroscopic tool, complementing the well established coherent inelastic neutron scattering (INS) technique for phonon dispersion investigations. In the study of crystalline systems IXS is a viable alternative to INS, especially in cases where only small samples are available. Using IXS, we have measured the phonon dispersion of Nd_{1.86}Ce_{0.14}CuO_{4+\delta} along the [x,0,0] and [x,x,0] in-plane directions. Compared to the undoped parent compound, the two highest longitudinal optical (LO) phonon branches are shifted to lower energies because of Coulomb-screening effects brought about by the doped charge carriers. An additional anomalous softening of the highest branch is observed around q=(0.2,0,0). This anomalous softening, akin to what has been observed in other compounds, provides evidence for a strong electron-phonon coupling in the electron-doped high-temperature superconductors.