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

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 $B_{2g}$ 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.

published in JPSJ

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