Coupled valence carrier and core-exciton dynamics in WS 2 probed by few-femtosecond extreme ultraviolet transient absorption spectroscopy

Hung-Tzu Chang (1) , Alexander Guggenmos (1) , Christopher T Chen (2) , Juwon Oh (1) , Romain Géneaux (3, 1) , Yi-De Chuang (2) , Adam M Schwartzberg (2) , Shaul Aloni (2) , Daniel M Neumark (1, 2) , Stephen R Leone (1, 2)

1 UC Berkeley - University of California [Berkeley]
2 LBNL - Lawrence Berkeley National Laboratory [Berkeley]
3 ATTO - Attophysique

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]

Hung-Tzu Chang, Alexander Guggenmos, Christopher T Chen, Juwon Oh, Romain Géneaux, et al.. Coupled valence carrier and core-exciton dynamics in WS 2 probed by few-femtosecond extreme ultraviolet transient absorption spectroscopy. Physical Review B, 2021, 104 (6), pp.064309. ⟨10.1103/PhysRevB.104.064309⟩. ⟨cea-04453383⟩