Coupled valence carrier and core-exciton dynamics in WS 2 probed by few-femtosecond extreme ultraviolet transient absorption spectroscopy
Résumé
Few-femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy, performed with optical 500-1000-nm supercontinuum and broadband XUV pulses (30-50 eV), simultaneously probes dynamics of photoexcited carriers in WS$_2$ at the WO$_3$ edge (37-45 eV) and carrier-induced modifications of core-exciton absorption at the W $N_{6,7}$ edge (32-37 eV). Access to continuous core-to-conduction-band absorption features and discrete core-exciton transitions in the same XUV spectral region in a semiconductor provides a means to investigate the effect of carrier excitation on core-exciton dynamics. The core-level transient absorption spectra, measured with either pulse arriving first to explore both core-level and valence carrier dynamics, reveal that coreexciton transitions are strongly influenced by the photoexcited carriers. A 1.2 ± 0.3 ps hole-phonon relaxation time and a 3.1 ± 0.4 ps carrier recombination time are extracted from the XUV transient absorption spectra from the core-to-conduction-band transitions at the W O$_3$ edge. Global fitting of the transient absorption signal at the W $N_{6,7}$ edge yields ∼10 fs coherence lifetimes of core-exciton states and reveals that the photoexcited carriers, which alter the electronic screening and band filling, are the dominant contributor to the spectral modifications of core excitons and direct field-induced changes play a minor role. This work provides a first look at the modulations of core-exciton states by photoexcited carriers and advances our understanding of carrier dynamics in metal dichalcogenides.
Domaines
Physique [physics]Origine | Fichiers éditeurs autorisés sur une archive ouverte |
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