Coupled valence carrier and core-exciton dynamics in WS₂ probed by few-femtosecond extreme ultraviolet transient absorption spectroscopy

Journal Article · 22 August 2021 · Physical Review B

DOI: https://doi.org/10.1103/physrevb.104.064309 · OSTI ID:1812349

Chang, Hung-Tzu  ^[1]; Guggenmos, Alexander  ^[1]; Chen, Christopher T.  ^[2]; Oh, Juwon  ^[1]; Géneaux, Romain  ^[1]; Chuang, Yi-De  ^[3]; Schwartzberg, Adam M. ^[2]; Aloni, Shaul ^[2]; Neumark, Daniel M.  ^[4]; Leone, Stephen R.  ^[4]

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1. Univ. of California, Berkeley, CA (United States)
2. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
4. Univ. of California, Berkeley, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

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 W O$$_3$$ 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 novel 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 core-exciton transitions are strongly influenced by the photoexcited carriers. A $$1.2\pm0.3$$ ps hole-phonon relaxation time and a $$3.1\pm0.4$$ 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 $$\sim 10$$ 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.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES), Scientific User Facilities Division
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1812349
• Journal Information: Physical Review B, Journal Name: Physical Review B Journal Issue: 6 Vol. 104; ISSN 2469-9950
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English