Ultrafast Transition from State-Blocking Dynamics to Electron Localization in Transition Metal β-Tungsten

Abstract

We describe an ultrafast transition of the electronic response of optically excited transition metal β-tungsten with few-femtosecond time resolution. The response moves from a regime where state filling of the excited carrier population around the Fermi level dominates towards localization of carriers onto the outer d orbitals. This is in contrast to previous measurements using ultrafast element-specific core-level spectroscopy enabled by attosecond transient absorption spectroscopy on transition metals such as titanium and around the transition metal atom in transition metal dichalchogenides MoTe2 and MoSe2. This surprisingly different dynamical response for β-tungsten can be explained by considering the electron-electron dynamics on a few-femtosecond timescale and the slower electron-phonon thermalization dynamics.