Mechanisms of High-Order Perturbative Photoemission from Cu(001)

Bisio, Francesco; Nývlt, M.; Franta, Jiří; Petek, Hrvoje; Kirschner, J.

doi:10.1103/physrevlett.96.087601

Cited by 67 publications

(74 citation statements)

References 21 publications

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“…This is contrary to perturbative mPP spectra of metals, where single electrons absorb m photons from the occupied bands so the maximum photoelectron energy appears at E F þ mhν. Moreover, if multiple orders of m appear in mPP spectra, the photoelectron yield strongly decreases with each higher order [68,69]. The increase of m with decreasing hν can be understood in the following way.…”

Section: Resultsmentioning

confidence: 99%

“…In ultrafast photoelectron imaging experiments using 10-100 times higher fluences, thermionic photoemission from graphite with T e that saturates at 18,000 K has already been deduced, but its origin has not been discussed [89]. In light of typical mPP spectra of metals, where dipole transitions rather than energy and momentum scattering play the dominant role in the photoemission process [68,69], the rapid thermalization in graphite raises the question of the mechanism for the nonlinear electron excitation in graphite.…”

Section: Resultsmentioning

confidence: 99%

“…Further excitation of the primary hot electron in the π Ã band is unlikely because there are no vertical bands above it within about 6 eV, where such transitions could terminate. Moreover, to be photoemitted, electrons must have sufficient kinetic energy in the surface-normal direction to overcome the surface potential [68]. Hot electrons near the K and M points, however, have most of their kinetic energy in the surface parallel motion and therefore cannot undergo photoemission after absorbing another photon, unless they also undergo momentum scattering.…”

Section: Resultsmentioning

confidence: 99%

“…The photoelectron yields are remarkably nonlinear with the laser fluence I, having power-law dependence I m , where m ranges from 2 to 8 as the excitation wavelength is tuned from UV to IR. High-order nonlinear mPP processes have been observed in metals in the perturbative and nonperturbative regimes of light-matter interaction, where electrons are promoted from occupied bands in an energy ladder-climbing process by absorbing multiple m quanta of light, hν, or are accelerated and released into the vacuum by the applied optical field [68][69][70]. By contrast, mPP in graphite occurs in an entirely different regime, where absorption of m quanta of light by the π-π Ã transition creates the primary hot electrons.…”

Section: Introductionmentioning

confidence: 99%

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Ultrafast Multiphoton Thermionic Photoemission from Graphite

et al. 2017

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Electronic heating of cold crystal lattices in nonlinear multiphoton excitation can transiently alter their physical and chemical properties. In metals where free electron densities are high and the relative fraction of photoexcited hot electrons is low, the effects are small, but in semimetals, where the free electron densities are low and the photoexcited densities can overwhelm them, the intense femtosecond laser excitation can induce profound changes. In semimetal graphite and its derivatives, strong optical absorption, weak screening of the Coulomb potential, and high cohesive energy enable extreme hot electron generation and thermalization to be realized under femtosecond laser excitation. We investigate the nonlinear interactions within a hot electron gas in graphite through multiphoton-induced thermionic emission. Unlike the conventional photoelectric effect, within about 25 fs, the memory of the excitation process, where resonant dipole transitions absorb up to eight quanta of light, is erased to produce statistical Boltzmann electron distributions with temperatures exceeding 5000 K; this ultrafast electronic heating causes thermionic emission to occur from the interlayer band of graphite. The nearly instantaneous thermalization of the photoexcited carriers through Coulomb scattering to extreme electronic temperatures characterized by separate electron and hole chemical potentials can enhance hot electron surface femtochemistry, photovoltaic energy conversion, and incandescence, and drive graphite-to-diamond electronic phase transition.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ultrafast Multiphoton Thermionic Photoemission from Graphite

et al. 2017

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“…10,11 At the same time, the multiphoton spectroscopy of the electronic states of the bulk continuum has received comparatively little attention. [12][13][14][15][16] The role of intermediate unoccupied states in these transitions has not been fully understood yet. Theoretical models on this issue mainly rely on density-matrix time evolution 17,18 and nonlinear-response treatments.…”

Section: Introductionmentioning

confidence: 99%

Direct resolution of unoccupied states in solids via two-photon photoemission

et al. 2008

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Nonlinear effects in photoemission are shown to open an access to the band structure of unoccupied states in solids, totally different from hitherto used photoemission spectroscopy. Despite its second-order nature, strong resonant transitions occur, obeying exact selection rules of energy, crystal symmetry, and momentum. Ab initio calculations are performed to demonstrate that such structures are present in low-energy laser spectroscopy experimental measurements on Si. Similar resonances are predicted in ultraviolet angle-resolved photoemission spectra, as shown with a theoretical calculation on bulk Al.

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Higher Order Photoemission from Metal Surfaces

Winkelmann

Chiang

Bisio

et al. 2010

Dynamics at Solid State Surfaces and Interfaces

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Photoemission spectroscopy (PES) is a widely employed method for mapping the electronic structure of solids [1,2]. In the simplest picture, the incident radiation induces transitions of electrons from occupied to unoccupied single-particle states separated by the photon energy. By invoking the laws of energy and momentum conservation, the photoemission process can be applied to map the occupied band structure of solids by detecting the photoelectrons in final states above the vacuum barrier.A generalization of the linear one-photon photoelectric effect can be realized by nonlinear multiphoton processes induced by ultrashort laser pulses of high intensity, where the occupied initial states, the unoccupied intermediate states, and the coupling between them play a central role. The unique power of these effects stems from the fact that the dynamical processes in the intermediate excited states become directly accessible in the time domain when using delayed excitation pulses. Especially the technique of time-resolved two-photon photoemission (2PPE) has been used to gain information on the decay rates of electronic populations and their dephasing times [3][4][5].Compared to 2PPE, higher order multiphoton photoemission processes (mPPE) in solids, which can extend the energy range of the studied unoccupied states and provide further information on photoexcitation processes, have received only little attention. This is mainly because their observation requires very intense optical fields and their considerably reduced photoelectron yields can be overwhelmed by space charge effects from the lower order processes [6][7][8][9][10][11][12][13][14][15]. Moreover, nonphotoelectric effect emission through the surface plasmon excitation and possibly tunneling, leading to ponderomotive acceleration of photoelectrons up to 0.4 keV energy [9,16], has been reported with comparatively low external fields. Therefore, the mechanisms for high-order photoelectric excitations at solid surfaces, in particular to what extent they are governed by the band structure of metals, are largely unexplored.

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Mechanisms of High-Order Perturbative Photoemission from Cu(001)

Cited by 67 publications

References 21 publications

Ultrafast Multiphoton Thermionic Photoemission from Graphite

Ultrafast Multiphoton Thermionic Photoemission from Graphite

Direct resolution of unoccupied states in solids via two-photon photoemission

Higher Order Photoemission from Metal Surfaces

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