  Electronic interactions associated with atomic adsorbates on transition metal
dichalcogenides such as MoS2 can induce massive electronic reconstruction that
results in the formation of a new type of heavily doped transition metal
dichalcogenide that exhibits characteristics of a two-dimensional electron gas.
The impact of quantum confinement and reduced dimensionality on the carrier
dynamics in such two-dimensional systems is at present not known, but is of
paramount importance if they are to find application in optoelectronic devices.
Here we show by a combination of angle-resolved photoemission and advanced
x-ray spectroscopies that many-body interactions in reduced dimension
drastically shorten carrier lifetimes to below 0.5 fs, and reveal how potassium
intercalation in MoS2 forces orbital rehybridization to create a
two-dimensional electron gas.
