Soft-phonon-driven superconductivity in CaAlSi as seen by inelastic x-ray scattering

TL;DR

This study combines inelastic x-ray scattering and ab initio calculations to reveal a soft phonon mode in CaAlSi, linking lattice dynamics directly to its superconducting properties.

Contribution

It provides the first detailed experimental and theoretical analysis of phonon behavior and electron-phonon coupling in CaAlSi, clarifying the role of soft phonons in its superconductivity.

Findings

Identification of a soft c-axis polarized phonon mode

Temperature-dependent phonon linewidth narrowing

Strong agreement between experiment and electron-phonon coupling calculations

Abstract

Inelastic x-ray scattering and $ab$-$initio$ calculation are applied to investigate the lattice dynamics and electron-phonon coupling of the ternary silicide superconductor CaAlSi ($P/bar{6}m2$). A soft c-axis polarized mode is clearly observed along the $/Gamma$-$A$-$L$ symmetry directions. The soft mode is strongly anharmonically broadened at room temperature, but, at 10 K, its linewidth narrows and becomes in good agreement with calculations of linear electron-phonon coupling. This establishes a coherent description of the detailed phonon properties in this system and links them clearly and consistently with the superconductivity.