Revealing the role of electrons and phonons in the ultrafast recovery of charge density wave correlations in 1$T$-TiSe$_2$

TL;DR

This study uses advanced spectroscopy to explore the ultrafast dynamics of charge density waves in 1T-TiSe2, revealing the roles of electrons and phonons in the phase recovery process and supporting a combined excitonic and electron-phonon mechanism.

Contribution

It provides new insights into the interplay of electron-hole correlations, excitonic effects, and phonons in the CDW phase dynamics of 1T-TiSe2.

Findings

Observation of coherent oscillation of the CDW amplitude mode

Identification of an ultrafast component in CDW recovery at 240 K

Support for a combined mechanism involving Coulomb interaction, excitonic insulator, and electron-phonon coupling

Abstract

Using time- and angle-resolved photoemission spectroscopy with selective near- and mid-infrared photon excitations, we investigate the femtosecond dynamics of the charge density wave (CDW) phase in 1$T$-TiSe$_2$, as well as the dynamics of CDW fluctuations at 240 K. In the CDW phase, we observe the coherent oscillation of the CDW amplitude mode. At 240 K, we single out an ultrafast component in the recovery of the CDW correlations, which we explain as the manifestation of electron-hole correlations. Our momentum-resolved study of femtosecond electron dynamics supports a mechanism for the CDW phase resulting from the cooperation between the interband Coulomb interaction, the mechanism of excitonic insulator phase formation, and electron-phonon coupling.