Electron-phonon coupling and superconductivity-induced distortion of the phonon lineshape in V$_3$Si

TL;DR

This study combines inelastic x-ray scattering and theoretical modeling to investigate how electron-phonon interactions influence phonon behavior and superconductivity in V$_3$Si, focusing on soft phonon modes near the structural and superconducting transition temperatures.

Contribution

It provides the first detailed temperature-dependent lattice dynamics analysis of V$_3$Si using inelastic x-ray scattering and density-functional-perturbation theory, highlighting the role of soft phonon modes in superconductivity.

Findings

Observation of a soft phonon mode at the structural transition temperature.

Theoretical prediction of electron-phonon coupling effects on lattice dynamics.

Explanation of superconductivity-induced phonon lineshape anomalies.

Abstract

Phonon measurements in the A15-type superconductors were complicated in the past because of the unavailability of large single crystals for inelastic neutron scattering, e.g., in the case of Nb$_3$Sn, or unfavorable neutron scattering properties in the case of V$_3$Si. Hence, only few studies of the lattice dynamical properties with momentum resolved methods were published, in particular below the superconducting transition temperature $T_c$. Here, we overcome these problems by employing inelastic x-ray scattering and report a combined experimental and theoretical investigation of lattice dynamics in V$_3$Si with the focus on the temperature-dependent properties of low-energy acoustic phonon modes in several high-symmetry directions. We paid particular attention to the evolution of the soft phonon mode of the structural phase transition observed in our sample at $T_s=18.9\,\rm{K}$, i.e., just above the measured superconducting phase transition at $T_c=16.8\,\rm{K}$. Theoretically, we predict lattice dynamics including electron-phonon coupling based on density-functional-perturbation theory and discuss the relevance of the soft phonon mode with regard to the value of $T_c$. Furthermore, we explain superconductivityinduced anomalies in the lineshape of several acoustic phonon modes using a model proposed by Allen et al., [Phys. Rev. B 56, 5552 (1997)].