Momentum-resolved observation of ultrafast interlayer charge transfer between the topmost layers of Mo S 2

How fast is the charge transfer between two layers of transition metal dichalcogenides and where does it take place in momentum space? Two-photon photoemission using high-harmonic probe pulses can answer this question, as the authors demonstrate here for the topmost layers of MoS${}_{2}$. By tuning pump pulses below the topmost-layer gap, they excite electrons in deeper layers and probe only the topmost layer. GW-based tight-binding calculations support the experimental findings and explain why the electron transfer takes place at $\\overline{\\mathrm{\\ensuremath{\\Sigma}}}$.