Abstract
We use the terahertz (THz) emission spectroscopy to study femtosecond photocurrent dynamics in the prototypical 2D semiconductor, transition metal dichalcogenide MoSe2. We identify several distinct mechanisms producing THz radiation in response to an ultrashort (30 fs) optical excitation in a bilayer (BL) and a multilayer (ML) sample. In the ML, the THz radiation is generated at a picosecond timescale by out-of-plane currents due to the drift of photoexcited charge carriers in the surface electric field. The BL emission is generated by an in-plane shift current. Finally, we observe oscillations at about 23 THz in the emission from the BL sample. We attribute the oscillations to quantum beats between two excitonic states with energetic separation of ∼100 meV.
Highlights
Manuscript’ watermark, but excluding any other editing, typesetting or other changes made by IOP Publishing and/or its licensors”
In the ML samples, the tilt angle dependence is more complex (Fig. S8), the electro-optic sampling (EOS) signal does not flip sign, which is expected for inplane generating current
We address the oscillations in the EOS signal
Summary
Manuscript’ watermark, but excluding any other editing, typesetting or other changes made by IOP Publishing and/or its licensors”. The large bandwidth of our experiment allows us to detect oscillations in the THz emission which we attribute to quantum beats between inter- and intra-layer excitonic states in MoSe2 [34,35,36].
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