Formation and Attosecond Carrier Dynamics of a Two-Dimensional Electron Gas in K/MoS2.

Electronic interactions associated with atomic adsorbates on transition metal dichalcogenides such as MoS2 can induce massive electronic reconstruction. This offers a powerful handle to tailor the electronic structure of this versatile materials class beyond changes of chemical composition or the creation of van der Waals heterostructures. To take full advantage of this approach, it is important to understand the mechanism and the consequences of the adsorbate-induced reconstruction for carrier dynamics. Here we show by a combination of angle-resolved photoemission and advanced x-ray spectroscopies that potassium intercalation in MoS2 creates a two-dimensional electron gas by forcing orbital rehybridization. The resulting electronic structure resembles that of a monolayer, and the resulting many-body interactions in reduced dimension drastically shorten carrier lifetimes to below 0.5 fs. Together, these observations provide evidence that K intercalation brings about the emergence of new quasi-two-dimensional electronic phases at the surface of a bulk transition metal dichalcogenide.