Speaker
Description
Coulomb-bound quasiparticles, such as excitons and trions in transition metal dichalcogenide monolayers, feature high binding energies on the order of 100s of meV, exhibit strong light-matter coupling, and can store quantum information in spin-valley degrees of freedom. Realizing strategies for external control of the excitonic states on ultrafast timescales thus emerged as an important avenue of research.
Here we discuss the observations of transient trion-to-exciton conversion in hBN-encapsulated MoSe$_2$ monolayer induced by intense THz pulses on picosecond timescales, generated at the infrared Free-Electron Laser facility (FELBE) [1]. The exciton dynamics are monitored by recording time-resolved photoluminescence (trPL) spectra with a streak camera which is synchronized at the repetition rate of the FEL. Visible pulses ($\lambda$ = 400 nm) excite a population of both excitons and trions. By adding THz pulses after about 30 picosecond delay with respect to the visible excitation, we observe a strong quenching of the trion emission and a temporary brightening of the exciton emission. Importantly, efficient trion-to-exciton conversion is observed when the THz photon energy is equal or higher than the trion binding energy.
Recently, we observed similar impact of THz radiation in other materials such as WSe$_2$ monolayers [2] and MoSe$_2$/WSe$_2$ heterostructures, that host more complex excitonic species such as charged biexcitons and interlayer excitons, respectively. Altogether, the results open promising pathways towards external control of many-particle states in low-dimensional materials.
References
[1] T. Venanzi, et al., Nat. Photonics, 18, 1344-1349 (2024)
[2] M. Cuccu, et al., Phys. Rev. B 112, 205302 (2025).
| Scientific Topics | Solid State Physics |
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