Excitonic and lattice contributions to the charge density wave in 1T−TiSe2 revealed by a phonon bottleneck

Hamoon Hedayat, Charles Sayers, Davide Bugini, Claudia Dallera, Daniel Wolverson, Tim Batten, Sara Karbassi, Sven Friedemann, Giulio Cerullo, Jasper van Wezel, Stephen Clark, Ettore Carpene, Enrico Da Como

Research output: Contribution to journalArticle

Abstract

Understanding collective electronic states such as superconductivity and charge density waves is pivotal for fundamental science and applications. The layered transition metal dichalcogenide 1T−TiSe2 hosts a unique charge density wave (CDW) phase transition whose origins are still not fully understood. Here, we present ultrafast time- and angle-resolved photoemission spectroscopy (TR-ARPES) measurements complemented by time-resolved reflectivity (TRR) which allows us to establish the contribution of excitonic and electron-phonon interactions to the CDW. We monitor the energy shift of the valence band (VB) and coupling to coherent phonons as a function of laser fluence. The VB shift, directly related to the CDW gap closure, exhibits a markedly slower recovery dynamics at fluences above Fth=60μJcm−2. This observation coincides with a shift in the relative weight of coherently coupled phonons to higher-frequency modes in TRR, suggesting a phonon bottleneck. Using a rate equation model, the emergence of a high-fluence bottleneck is attributed to an abrupt reduction in coupled phonon damping and an increase in exciton dissociation rate linked to the loss of CDW superlattice phonons. Thus, our work establishes the important role of both excitonic and phononic interactions in the CDW phase transition and the advantage of combining complementary femtosecond techniques to understand the complex interactions in quantum materials.
Original languageEnglish
Article number 023029
JournalPhysical Review Research
Volume1
Issue number2
Early online date26 Sep 2019
DOIs
Publication statusPublished - 30 Sep 2019

Cite this

Excitonic and lattice contributions to the charge density wave in 1T−TiSe2 revealed by a phonon bottleneck. / Hedayat, Hamoon; Sayers, Charles; Bugini, Davide; Dallera, Claudia; Wolverson, Daniel; Batten, Tim; Karbassi, Sara; Friedemann, Sven; Cerullo, Giulio; van Wezel, Jasper; Clark, Stephen; Carpene, Ettore; Da Como, Enrico.

In: Physical Review Research, Vol. 1, No. 2, 023029, 30.09.2019.

Research output: Contribution to journalArticle

Hedayat, H, Sayers, C, Bugini, D, Dallera, C, Wolverson, D, Batten, T, Karbassi, S, Friedemann, S, Cerullo, G, van Wezel, J, Clark, S, Carpene, E & Da Como, E 2019, 'Excitonic and lattice contributions to the charge density wave in 1T−TiSe2 revealed by a phonon bottleneck', Physical Review Research, vol. 1, no. 2, 023029. https://doi.org/10.1103/PhysRevResearch.1.023029
Hedayat, Hamoon ; Sayers, Charles ; Bugini, Davide ; Dallera, Claudia ; Wolverson, Daniel ; Batten, Tim ; Karbassi, Sara ; Friedemann, Sven ; Cerullo, Giulio ; van Wezel, Jasper ; Clark, Stephen ; Carpene, Ettore ; Da Como, Enrico. / Excitonic and lattice contributions to the charge density wave in 1T−TiSe2 revealed by a phonon bottleneck. In: Physical Review Research. 2019 ; Vol. 1, No. 2.
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AU - Friedemann, Sven

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