Time-resolved XUV ARPES with tunable 24–33 eV laser pulses at 30 meV resolution

Sie, Edbert J.; Rohwer, Timm; Lee, Changmin; Gedik, Nuh

doi:10.1038/s41467-019-11492-3

Cited by 99 publications

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“…The observed polarization properties and their doping dependence can be understood from the band structure of t-WSe 2 =WSe 2 bilayers. In natural (2H) bilayer WSe 2 , recent angle-resolved photoemission spectroscopy measurements [61,62] and density functional theory calculations [27,63] suggest that the conduction band minimum (CBM) and valence band maximum (VBM) are located at the Q and K points, respectively. Our results suggest that these band extrema are conserved in t-WSe 2 =WSe 2 , consistent with recent studies in 3R-stacked bilayer WS 2 [64].…”

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confidence: 99%

Electrically Tunable Valley Dynamics in Twisted WSe2/WSe2 Bilayers

et al. 2020

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The twist degree of freedom provides a powerful new tool for engineering the electrical and optical properties of van der Waals heterostructures. Here, we show that the twist angle can be used to control the spin-valley properties of transition metal dichalcogenide bilayers by changing the momentum alignment of the valleys in the two layers. Specifically, we observe that the interlayer excitons in twisted WSe 2 =WSe 2 bilayers exhibit a high (>60%) degree of circular polarization (DOCP) and long valley lifetimes (>40 ns) at zero electric and magnetic fields. The valley lifetime can be tuned by more than 3 orders of magnitude via electrostatic doping, enabling switching of the DOCP from ∼80% in the n-doped regime to <5% in the p-doped regime. These results open up new avenues for tunable chiral light-matter interactions, enabling novel device schemes that exploit the valley degree of freedom.

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Electrically Tunable Valley Dynamics in Twisted WSe2/WSe2 Bilayers

et al. 2020

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“…Our results discussed here are based on numerical simulations. To measure the sub-optical cycle evolution of the light-induced electron dynamics at optical frequencies directly, time-and angle-resolved photoemission spectroscopy (trARPES) is required, which becomes nowadays feasible using attosecond pulses [51]. Recently, such electron dynamics, driven with terahertz pulses at topological surface states in Bi 2 Te 3 , have been measured using UV pulses as a probe [5].…”

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Sub-cycle temporal evolution of light-induced electron dynamics in hexagonal 2D materials

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Two-dimensional materials with hexagonal symmetry such as graphene and transition metal dichalcogenides are unique materials to study light-field-controlled electron dynamics inside of a solid. Around the K-point, the dispersion relation represents an ideal system to study intricately coupled intraband motion and interband (Landau-Zener) transitions driven by the optical field of phase-controlled few-cycle laser pulses. Based on the coupled nature of the intraband and interband processes, we have recently observed in graphene repeated coherent Landau-Zener transitions between valence and conduction band separated by around half an optical period of 1.3 fs (Higuchi et al Nature 550, 224 (2017)). Due to the low temporal symmetry of the applied laser pulse, a residual current density and a net electron polarization are formed. Here we show extended numerical data on the temporal evolution of the conduction band population of 2D materials with hexagonal symmetry during the light-matter interaction, yielding deep insights to attosecond-fast electron dynamics. In addition, we show that a residual ballistic current density is formed, which strongly increases when a band gap is introduced. Both, the sub-cycle electron dynamics and the resulting residual current are relevant for the fundamental understanding and future applications of strongly driven electrons in two-dimensional materials, including graphene or transition metal dichalcogenide monolayers.

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“…A more detailed description of the monochromator is also provided in Ref. 28. The gold-coated grating has 500 grooves per mm (Richardson gratings) and it is mounted in an "off-plane" geometry so that the rulings are oriented parallel to the propagation direction of the beam.…”

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confidence: 99%

High resolution time- and angle-resolved photoemission spectroscopy with 11 eV laser pulses

Lee

Rohwer

Sie

et al. 2020

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Performing time and angle resolved photoemission spectroscopy (tr-ARPES) at high momenta necessitates extreme ultraviolet laser pulses, which are typically produced via high harmonic generation (HHG). Despite recent advances, HHG-based setups still require large pulse energies (hundreds of µ J to mJ) and their energy resolution is limited to tens of meV. Here, we present a novel 11 eV tr-ARPES setup that generates a flux of 5× 10 10 photons/s and achieves an unprecedented energy resolution of 16 meV. It can be operated at high repetition rates (up to 250 kHz) while using input pulse energies down to 3 µ J. We demonstrate these unique capabilities by simultaneously capturing the energy and momentum

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Time-resolved XUV ARPES with tunable 24–33 eV laser pulses at 30 meV resolution

Cited by 99 publications

References 65 publications

Electrically Tunable Valley Dynamics in Twisted WSe2/WSe2 Bilayers

Electrically Tunable Valley Dynamics in Twisted WSe2/WSe2 Bilayers

Sub-cycle temporal evolution of light-induced electron dynamics in hexagonal 2D materials

High resolution time- and angle-resolved photoemission spectroscopy with 11 eV laser pulses

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