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The transition metal dichalcogenide IrTe$_2$ undergoes two first-order structural and charge-ordered phase transitions on cooling below 270 K and below 180 K. It has been put forward that a Mott phase involving spin-orbit-coupled states [1] may be at the origin of the phase transitions in IrTe$_2$.
Here we present a time-resolved angle-resolved photoelectron spectroscopy study of IrTe$_2$ [2]. The possibility of inducing a phase transition by photoexcitation with near-infrared femtosecond pulses is investigated in the charge-ordered phases. We observe changes of the spectral function occurring within a few hundreds of femtoseconds and persisting up to several picoseconds, which we interpret as a partial photoinduced phase transition (PIPT). The necessary time for photoinducing these spectral changes increases with increasing photoexcitation density and reaches time scales longer than the rise time of the transient electronic temperature. We conclude that the PIPT is driven by a transient increase of the lattice temperature following the energy transfer from the electrons. However, the photoinduced changes of the spectral function are small, which indicates that the low-temperature phase is particularly robust against photoexcitation. We suggest that the system might be trapped in an out-of-equilibrium state, for which only a partial structural transition is achieved.
[1] K.-T. Ko et al., Nat. Commun. 6, 7343 (2015).
[2] C. Monney, A. Schuler, T. Jaouen, M.-L. Mottas, Th. Wolf, M. Merz, M. Muntwiler, L. Castiglioni, P. Aebi, F. Weber and M. Hengsberger, Phys. Rev. B 97, 075110 (2018).
