Ultrafast dynamics in photoexcited valence-band states of Si studied by time- and angle-resolved photoemission spectroscopy of bulk direct transitions

Kanasaki, J.; Tanimura, Hiroshi; Tanimura, Katsumi; Ries, Philip; Heckel, Wolfgang; Biedermann, K.; Fauster, Thomas

doi:10.1103/physrevb.97.035201

Cited by 8 publications

(8 citation statements)

References 36 publications

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“…For comparison, previous experiments of polycrystalline TMDC monolayers on metal or graphene substrates show lifetimes up to four-orders of magnitude shorter [17,18]. Thus, the band renormalization determined here reflects close-to intrinsic manybody interactions in the MoS2 monolayer [30]. The time dependent band renormalization quantified in our TR-ARPES measurement is also in qualitative agreement with previous optical measurements on monolayer TMDCs [7,8,11,[35][36][37].…”

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Direct Determination of Band Gap Renormalization in Photo-Excited Monolayer Mos2

Liu¹,

Ziffer²,

Hansen³

et al. 2019

Proceedings of the 74th International Symposium on Molecular Spectroscopy

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A key feature of monolayer semiconductors, such as transition-metal dichalcogenides, is the poorly screened Coulomb potential, which leads to large exciton binding energy (Eb) and strong renormalization of the quasiparticle bandgap (Eg) by carriers. The latter has been difficult to determine due to cancellation in changes of Eb and Eg, resulting in little change in optical transition energy at different carrier densities. Here we quantify bandgap renormalization in macroscopic single crystal MoS2 monolayers on SiO2 using time and angle resolved photoemission spectroscopy (TR-ARPES). At excitation density above the Mott threshold, Eg decreases by as much as 360 meV. We compare the carrier density dependent Eg with previous theoretical calculations and show the necessity of knowing both doping and excitation densities in quantifying the bandgap. Atomically thin transition-metal dichalcogenide (TMDC) monolayers and heterojunctions are being broadly explored as model systems for a wide range of electronic, optoelectronic, and quantum processes. The commonly studied TMDC monolayers possess direct bandgaps in the visible to near-IR region [1-3]. Because of the strong many-body Coulomb interactions in monolayer TMDCs, both exciton binding energy (Eb) and bandgap renormalization energy are large [3]. The former lowers the optical transition energy by hundreds meV from Eg, while the latter decreases Eg by similar amounts in the presence of charge carriers or excitons. The bandgap renormalization energy (DEg) and decrease in exciton binding energy (DEb) tend to be of similar magnitudes but counteract each other, leading to comparatively modest changes in optical transition energies [4,5]. Since the quasiparticle bandgap Eg is the most fundamental quantity and

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“…Thus, the up-shift in VBM and broadening of the valence band results from manybody effects resulting from the excitation. The former measures the band renormalization [4,6,7] and the latter attributed to dephasing from holehole scattering [30].…”

mentioning

confidence: 99%

Direct Determination of Band Gap Renormalization in Photo-Excited Monolayer Mos2

Liu¹,

Ziffer²,

Hansen³

et al. 2019

Proceedings of the 74th International Symposium on Molecular Spectroscopy

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“…The time resolution of PEEM can be extended from second to potentially attosecond time scales when it is combined with pulsed laser sources. ,,, In such experiment, a pump pulse initiates a change or induces a field, and a delayed probe pulse records its spatiotemporal evolution by exciting photoemission by single or multiphoton absorption. If absorption of two or more photons is necessary to excite electrons above E vac , such nonlinear pump–probe methods are particularly useful to study the excited state spatiotemporal polarization , and population dynamics. , Pump–probe methods can also be used in experiments where the pump generates a nonthermal or hot thermal electron population, and the probe laser uses one-photon photoemission (1PP) to measure a change in the Fermi distribution of electrons within a sample. − Because the time resolution in such experiments only depends on the optical system, i.e., it is independent of the PEEM instrument, it can potentially reach the attosecond time scale by just combining the existing laser and PEEM instrumentation, as will be discussed further.…”

Section: Imaging Plasmons With Peemmentioning

confidence: 99%

Ultrafast Photoemission Electron Microscopy: Imaging Plasmons in Space and Time

2020

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Plasmonics is a rapidly growing field spanning research and applications across chemistry, physics, optics, energy harvesting, and medicine. Ultrafast photoemission electron microscopy (PEEM) has demonstrated unprecedented power in the characterization of surface plasmons and other electronic excitations, as it uniquely combines the requisite spatial and temporal resolution, making it ideally suited for 3D space and time coherent imaging of the dynamical plasmonic phenomena on the nanofemto scale. The ability to visualize plasmonic fields evolving at the local speed of light on subwavelength scale with optical phase resolution illuminates old phenomena and opens new directions for growth of plasmonics research. In this review, we guide the reader thorough experimental description of PEEM as a characterization tool for both surface plasmon polaritons and localized plasmons and summarize the exciting progress it has opened by the ultrafast imaging of plasmonic phenomena on the nanofemto scale.

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Direct Determination of Band-Gap Renormalization in the Photoexcited Monolayer MoS2

et al. 2019

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A key feature of monolayer semiconductors, such as transition-metal dichalcogenides, is the poorly screened Coulomb potential, which leads to large exciton binding energy (E b ) and strong renormalization of the quasiparticle bandgap (E g ) by carriers. The latter has been difficult to determine due to cancellation in changes of E b and E g , resulting in little change in optical transition energy at different carrier densities. Here we quantify bandgap renormalization in macroscopic single crystal MoS 2 monolayers on SiO 2 using time and angle resolved photoemission spectroscopy (TR-ARPES). At excitation density above the Mott threshold, E g decreases by as much as 360 meV. We compare the carrier density dependent E g with previous theoretical calculations and show the necessity of knowing both doping and excitation densities in quantifying the bandgap. Atomically thin transition-metal dichalcogenide (TMDC) monolayers and heterojunctions are being broadly explored as model systems for a wide range of electronic, optoelectronic, and quantum processes. The commonly studied TMDC monolayers possess direct bandgaps in the visible to near-IR region [1-3]. Because of the strong many-body Coulomb interactions in monolayer TMDCs, both exciton binding energy (E b ) and bandgap renormalization energy are large [3]. The former lowers the optical transition energy by hundreds meV from E g , while thelatter decreases E g by similar amounts in the presence of charge carriers or excitons. The bandgap renormalization energy (ΔE g ) and decrease in exciton binding energy (ΔE b ) tend to be of similar magnitudes but counteract each other, leading to comparatively modest changes in optical transition energies [4,5]. Since the quasiparticle bandgap E g is the most fundamental quantity and is predicted to be exceptionally sensitive to carrier or exciton densities [4,6,7], there

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Ultrafast dynamics in photoexcited valence-band states of Si studied by time- and angle-resolved photoemission spectroscopy of bulk direct transitions

Cited by 8 publications

References 36 publications

Direct Determination of Band Gap Renormalization in Photo-Excited Monolayer Mos2

Direct Determination of Band Gap Renormalization in Photo-Excited Monolayer Mos2

Ultrafast Photoemission Electron Microscopy: Imaging Plasmons in Space and Time

Direct Determination of Band-Gap Renormalization in the Photoexcited Monolayer MoS2

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