Abstract
The layered transition-metal dichalcogenide MoS${}_{2}$ as well as related compounds, such as WS${}_{2}$ and WSe${}_{2}$, undergo a transition from an indirect to a direct band-gap semiconductor when thinned down to a single layer. This unexpected observation, which goes along with substantial changes in electronic and optical properties, has stimulated numerous recent studies on this compound class, including pump-probe time-domain studies addressing fundamental aspects of hot carrier relaxation. So far, mainly all-optical methods have been applied to probe the ultrafast dynamics in a rather comprehensive manner. Due to intermixing of different processes and a lack of momentum-resolution, the interpretation of such data is, however, not necessarily straightforward. In order to complement these studies, the authors present here results of a time- and angle-resolved photoemission (trARPES) experiment on bulk MoS${}_{2}$, a technique that provides the most direct view onto hot electron dynamics in energy and momentum space. Surprisingly, the new data agree well with past results of monolayer MoS${}_{2}$ as opposed to bulk MoS${}_{2}$. The authors interpret this finding in terms of the high density of surface defects in MoS${}_{2}$ samples, which substantially affect hot carrier relaxation due to trapping. In contrast to all optical studies, trARPES is very efficient in probing such processes owing to the extreme surface sensitivity of photoemission.
Published Version
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