By means of time- and angle-resolved photoemission spectroscopy (tr-ARPES), we investigate the effect of the charge density wave (CDW) phase transition on the equilibrium and out-of-equilibrium electronic properties of the transition metal dichalcogenide VSe₂. The electronic band structure of VSe₂ has recently been subject of investigation for both bulk and monolayer samples, in search for the manifestation of the opening of the band gap in its CDW phase [1,2]. However, at present, only a few studies on the effect of an ultrafast optical excitation are available [1,3]. In our contribution we present a study on the bulk material. By selecting the polarization of the probe pulses, equilibrium ARPES allows us to visualize states with different orbital character, originating from the V and Se valence bands. In addition, tr-ARPES experiments unveil the emergence of a new state at the Fermi level induced by the pump pulse and lasting for several picoseconds after photoexcitation. In order to describe the rearrangement of the electronic population induced by the pump pulse, an ad hoc model has been developed. This model, based on four rate equations, allowed us for successfully describing the electron dynamics observed in vicinity of the Fermi level. When moving across the critical temperature of the CDW phase transition, our tr-ARPES data show indication for a change in the fast relaxation dynamics and for a different filling of the photoinduced state near the Fermi level.
 
[1] Biswas et al., Nano Letters 21, 1968-1975 (2021).
[2] Umemoto et al., Nano Research 12, 165-169 (2019).
[3] Majchrzak et al., Physical Review B 103, L241108 (2021).

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