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New scientific highlights- by MUST PIs Chergui, Milne, Wörner, Vaníček and Röthlisberger

Structural involvement in the melting of the charge density wave in 1T−TiSe2

March 1, 2021

It is commonly assumed that electronic phenomena occur at faster time scales than structural rearrangements. Here, we show the opposite: weak electronic excitations induce atomic displacements that outpace purely electronic charge carrier-interactions and hence are the dominant contribution in melting of the charge-density wave (CDW) in TiSe2. This divergence of electronic and structural order is directly observed in experimental data from a transient ultrafast resonant/non-resonant X-Ray diffraction experiment. Our results create a  paradigm shift that constitute a different, mechanistic pathway for phase transitions in the ultrafast regime.

Fig. 1. CDW phase and associated PLD upon cooling of 1TTiSe2. (a) Simplified Fermi surface of a slice through Fermi pockets of holes (red, Se 4p) and electrons (blue, Ti 3d) in the first Brillouin zone at ±A along the kc axis, shown in the room-temperature (left) and CDW (right) phase. The band-folding of Ti 3d and Se 4p states accompanying the CDW transition is indicated, leading to a re-referencing of the Brillouin zone (e.g., the RT L point becomes CDW L/Γ point). (b) The 3D representation of the bands illustrates the pd splitting between the folded Se 4p and Ti 3d bands at L/Γ, leading to excitonic correlations between electron-hole pairs (black dotted circle). (c) PLD associated with the CDW phase, causing a doubling of the unit cell along all three dimensions.
Reference: Burian, M., Porer, M., Mardegan, J.R.L., Esposito, V., Parchenko, S., Burganov, B., Gurung, N., Ramakrishnan, M., Scagnoli, V., Ueda, H., Francoual, S., Fabrizi, F., Tanaka, Y., Togashi, T., Kubota, Y., Yabashi, M., Rossnagel, K., Johnson, S.L., and Staub, U. (2021). Structural involvement in the melting of the charge density wave in 1T−TiSe2. Phys Rev Research 3, 013128. (10.1103/PhysRevResearch.3.013128)

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