Kavli Affiliate: Alessandra Lanzara
| First 5 Authors: Maximilian Huber, Yi Lin, Nicholas Dale, Renee Sailus, Sefaattin Tongay
| Summary:
The formation of a charge density wave state is characterized by an order
parameter. The way it is established provides unique information on both the
role that correlation plays in driving the charge density wave formation and
the mechanism behind its formation. Here we use time and angle resolved
photoelectron spectroscopy to optically perturb the charge-density phase in
1T-TiSe$_2$ and follow the recovery of its order parameter as a function of
energy, momentum and excitation density. Our results reveal that two distinct
orders contribute to the gap formation, a CDW order and pseudogap-like order,
manifested by an overall robustness to optical excitation. A detailed analysis
of the magnitude of the the gap as a function of excitation density and delay
time reveals the excitonic long-range nature of the CDW gap and the short-range
Jahn-Teller character of the pseudogap order. In contrast to the gap, the
intensity of the folded Se$_{4p}$* band can only give access to the excitonic
order. These results provide new information into the the long standing debate
on the origin of the gap in TiSe$_2$ and place it in the same context of other
quantum materials where a pseudogap phase appears to be a precursor of
long-range order.
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