Elastic Soft Mode and Electric Quadrupole Response in Excitonic Insulator Candidate (Ta$_{0.952}$V$_{0.048}$)$_2$NiSe$_5$: Contribution of Electron-Phonon Interaction

TL;DR

This study investigates the role of acoustic phonons and electron-phonon interactions in the excitonic transition of (Ta$_{0.952}$V$_{0.048}$)$_2$NiSe$_5$, revealing phonon softening and their contribution to the transition.

Contribution

It provides new insights into how electron-phonon interactions influence the excitonic transition in NiSe$_5$-based materials.

Findings

Observation of elastic constant softening indicating phonon soft mode.

Electron-phonon interaction contributes to the excitonic transition.

Analysis suggests hybridization and phonons both play roles in the transition.

Abstract

We performed ultrasonic measurements on (Ta$_{0.952}$V$_{0.048}$)$_2$NiSe$_5$ to investigate the contribution of acoustic phonons at the zone center to structural and possible excitonic transitions. The transverse elastic constant $C_{55}$ with irreducible representation $B_\mathrm{2g}$ exhibits softening over 90\% above a transition temperature of $T_\mathrm{s} = 280$ K, indicating the soft mode of corresponding TA phonons. Our analysis based on the quadrupole response indicates that the electron-phonon interaction contributes to the excitonic transition in addition to the hybridization between the conduction and valence bands if the excitonic transition is realized.