Intervalley scattering in MoS2 imaged by two-photon photoemission with a high-harmonic probe

Wallauer, R.; Reimann, J.; Armbrust, Nico; Güdde, J.; Höfer, U.

doi:10.1063/1.4965839

Cited by 71 publications

(58 citation statements)

References 40 publications

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“…The relative intensities are listed in table II. The best results were obtained with argon, even though krypton is expected to yield a stronger single-atom response 14,63 . It is possible that the higher ionization in the case of Kr prevented phase matching at the pulse peak, resulting in a shorter coherence length.…”

Section: E Comparison Between Different Nozzles and Noble Gasesmentioning

confidence: 99%

Time- and angle-resolved photoemission spectroscopy of solids in the extreme ultraviolet at 500 kHz repetition rate

Puppin

Deng

Nicholson

et al. 2019

Review of Scientific Instruments

114

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Time-and angle-resolved photoemission spectroscopy (trARPES) employing a 500 kHz extreme-ultraviolet (XUV) light source operating at 21.7 eV probe photon energy is reported. Based on a high-power ytterbium laser, optical parametric chirped pulse amplification (OPCPA), and ultraviolet-driven high-harmonic generation, the light source produces an isolated high-harmonic with 110 meV bandwidth and a flux of more than 10 11 photons/second on the sample. Combined with a stateof-the-art ARPES chamber, this table-top experiment allows high-repetition rate pump-probe experiments of electron dynamics in occupied and normally unoccupied (excited) states in the entire Brillouin zone and with a temporal system response function below 40 fs. function A(k,ω) and a matrix element between the initial and final state |M k if | 2 ; here k and ω denote the electron's wavevector and angular frequency, respectively. Many-body effects are encoded in the spectral function A(k,ω) and manifest themselves in renormalization of the bare electronic bands and in the observed lineshape 1 . In a trARPES experiment, the distribution I(k,ω) is collected for a series of delays (τ ) between pump and probe pulses: after perturbation, the population distribution f(k,ω,τ ) evolves towards a quasi-thermal distribution and energetically relaxes on femto-to picosecond timescales 2 . During relaxation, the concomitant many-body interactions affect the transient spectral function A(k,ω,τ ) and even the photoemission matrix elements might change, if the final state's orbital symmetry is altered 3 . trARPES accesses at once the population dynamics, the evolution of the spectral function and the evolution of matrix elements. trARPES has found increasingly successful applications in the past few decades 4-6 : among many examples, trARPES was used to study photo-induced phase transitions 7-11 and to observe electronic states above the Fermi level, unoccupied under equilibrium conditions [12][13][14][15][16] . Energy conservation in the photoemission processes imposes that a femtosecond light source for trARPES must possess a photon energy ω ph exceeding the work function Φ, which in most materials lies in the range between 4 to 6 eV. Ultraviolet femtosecond light sources are thus required for these experiments.The conservation of the electrons' in-plane momentum ( k ) in the photoemission process allows reciprocal space resolution. The advantage of a probe with high photon energy is Journal of Electron Spectroscopy and Related Phenomena 200, 15 (2015). 79 SPECS Surface Nano Analysis GmbH, product spectrometer PHOIBOS TM 150 (2013), see

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Section: E Comparison Between Different Nozzles and Noble Gasesmentioning

confidence: 99%

Time- and angle-resolved photoemission spectroscopy of solids in the extreme ultraviolet at 500 kHz repetition rate

Puppin

Deng

Nicholson

et al. 2019

Review of Scientific Instruments

114

View full text Add to dashboard Cite

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“…This makes TMDCs ideal candidates to observe exciton signatures in photoemission measurements. While excitons in indirect gap semiconductors cannot be resonantly photoexcited due to violation of conservation of momentum, they may be indirectly formed via intervalley scattering 27 .…”

Section: Introductionmentioning

confidence: 99%

Photoemission signature of excitons

Rustagi

Kemper

2018

Phys. Rev. B

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Excitons -the particle-hole bound states -composed of localized electron-hole states in semiconducting systems are crucial to explaining the optical spectrum. Spectroscopic measurements can contain signatures of these two particle bound states and can be particularly useful in determining the characteristics of these excitons. We formulate an expression for evaluating the angle-resolved photoemission spectrum arising from the ionization of excitons given their steady-state distribution in a semiconductor. We show that the spectrum contains information about the direct/indirect band gap nature of the semiconductor and is located below the conduction band minimum displaced by the binding energy. The dispersive features of the spectrum contains remnants of the valence band while additional interesting features arise from different exciton distributions. Our results indicate that for most exciton probability distributions, the energy integrated photoemission spectrum provides an estimate of the exciton Bohr radius.

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“…Such control combined with microscopic understanding of electron dynamics, as provided here, are crucial for conceiving TMDC-based spintronic device concepts. Recently, two studies reporting ultrafast electron dynamics in the related compound MoS 2 were published [36,37]. This work was funded by the Max Planck Society, the European Research Council (ERC-2010-AdG-267374), by the Ministerio de Economía y Competitividad (FIS2013-46159-C3-1-P), and Grupos Consolidados UPV/EHU (IT578-13).…”

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confidence: 99%

Generation and Evolution of Spin-, Valley-, and Layer-Polarized Excited Carriers in Inversion-Symmetric WSe2

et al. 2016

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We report the spin-selective optical excitation of carriers in inversion-symmetric bulk samples of the transition metal dichalcogenide (TMDC) WSe 2 . Employing time-and angle-resolved photoelectron spectroscopy (trARPES) and complementary time-dependent density functional theory (TDDFT), we observe spin-, valley-, and layer-polarized excited state populations upon excitation with circularly polarized pump pulses, followed by ultrafast (< 100 fs) scattering of carriers towards the global minimum of the conduction band. TDDFT reveals the character of the conduction band, into which electrons are initially excited, to be two-dimensional and localized within individual layers, whereas at the minimum of the conduction band, states have a three-dimensional character, facilitating interlayer charge transfer. These results establish the optical control of coupled spin-, valley-, and layer-polarized states in centrosymmetric materials with locally broken symmetries and suggest the suitability of TMDC multilayer and heterostructure materials for valleytronic and spintronic device concepts. DOI: 10.1103/PhysRevLett.117.277201 Manipulation of spin and valley degrees of freedom is a key step towards realizing novel quantum technologies [1][2][3][4], for which semiconducting two-dimensional (2D) TMDCs have been established as promising candidates. In monolayer TMDCs, the lack of inversion symmetry in 2H polytypes gives rise to a spin-valley correlation of the band structure which, in combination with strong spin-orbit coupling in those containing heavy transition metals [5], lifts the energy degeneracy of electronic bands of opposite spin polarizations, allowing for valley-selective electronic excitation with circularly polarized light [1,2,[5][6][7][8]. While such an effect should be forbidden in inversion symmetric materials, recent theoretical work suggests that the absence of inversion symmetry within moieties of the unit cell locally lifts the spin degeneracy [9,10]. The lack of inversion symmetry and the presence of in-plane dipole moments within individual TMDC layers can be seen as atomic site Dresselhaus and Rashba effects and can cause a hidden spin texture in a globally inversion symmetric material [9]. This is supported by the observation of spin-polarized valence bands in 2H-WSe 2 by photoelectron spectroscopy [11] and spin-resolved ARPES [12]. Polarization-resolved photoluminescence experiments on inversion-symmetric bilayer samples [1,2,[13][14][15] have shown varying degrees of circular dichroism. This has primarily been explained by symmetry breaking induced by applied or intrinsic electric and magnetic fields.In this Letter, we demonstrate that in centrosymmetric samples of 2H-WSe 2 , it is possible to generate spin-, valley-and layer-polarized excited states in the conduction band. By employing time-and angle-resolved photoemission spectroscopy (trARPES) with circularly polarized pump pulses, we observe spin-polarized excited state populations in the K valleys, which are in addition localized to a single...

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Intervalley scattering in MoS2 imaged by two-photon photoemission with a high-harmonic probe

Cited by 71 publications

References 40 publications

Time- and angle-resolved photoemission spectroscopy of solids in the extreme ultraviolet at 500 kHz repetition rate

Time- and angle-resolved photoemission spectroscopy of solids in the extreme ultraviolet at 500 kHz repetition rate

Photoemission signature of excitons

Generation and Evolution of Spin-, Valley-, and Layer-Polarized Excited Carriers in Inversion-Symmetric WSe2

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