# Revealing the role of electrons and phonons in the ultrafast recovery of charge density wave correlations in $1T−TiSe_2$

Monney, C; Puppin, M; Nicholson, C W; Hoesch, M; Chapman, R. T; Springate, E; Berger, H; Magrez, A; Cacho, C; Ernstorfer, R; Wolf, M (2016). Revealing the role of electrons and phonons in the ultrafast recovery of charge density wave correlations in $1T−TiSe_2$. Physical Review B, 94(16):165165.

## Abstract

Using time- and angle-resolved photoemission spectroscopy with selective near- and midinfrared photon excitations, we investigate the femtosecond dynamics of the charge density wave (CDW) phase in $1T−TiSe_2$ 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.

## Abstract

Using time- and angle-resolved photoemission spectroscopy with selective near- and midinfrared photon excitations, we investigate the femtosecond dynamics of the charge density wave (CDW) phase in $1T−TiSe_2$ 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.

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Item Type: Journal Article, refereed, original work 07 Faculty of Science > Physics Institute 530 Physics English 2016 11 Jan 2017 18:02 11 Jan 2017 18:02 American Physical Society 2469-9950 https://doi.org/10.1103/PhysRevB.94.165165

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