Ultrafast pseudospin dynamics in graphene

Grupp, Alexander; Trushin, Maxim; Soavi, Giancarlo; Budweg, Arne; Fazio, Domenico De; Lombardo, Antonio; Sassi, Ugo; Ferrari, Andrea C.; Belzig, Wolfgang; Leitenstorfer, Alfred; Brida, Daniele

doi:10.1103/physrevb.92.165429

Cited by 55 publications

(53 citation statements)

References 57 publications

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“…In parallel with e-e scattering, e-p scattering makes the carrier distributions more isotropic [46]. Although momentum transfers in e-p scattering can be large, the energy transfers are limited by the frequency of optical phonons [6,34,45].…”

Section: Introductionmentioning

confidence: 99%

“…Hot electron dynamics in graphene and graphite have been investigated by optical, THz, photoemission, and theoretical methods [1][2][3][4][5][6][7][8][9]23,34,[39][40][41][42][43][44][45][46]. Xu et al [39] first applied ultrafast time-resolved two-photon photoemission (TR-2PP) spectroscopy to excite a hot electron population and monitor its energy-dependent decay in graphite.…”

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: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Ultrafast Multiphoton Thermionic Photoemission from Graphite

et al. 2017

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“…The existence of anisotropic photocarrier distributions in graphene was predicted [1,2] and observed in optical pump-probe experiments [3][4][5][6], which showed a pronounced difference in the time-dependent optical response for different probe polarizations. The decay of the anisotropy extracted in this manner was attributed to optical phonon emission [2][3][4][5]7,8].…”

mentioning

confidence: 99%

“…The decay of the anisotropy extracted in this manner was attributed to optical phonon emission [2][3][4][5]7,8]. However, a complete picture for these nonequilibrium phenomena can only be obtained by tracking both carrier energy and momentum in the time domain.…”

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confidence: 99%

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Ultrafast momentum imaging of pseudospin-flip excitations in graphene

et al. 2017

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The pseudospin of Dirac electrons in graphene manifests itself in a peculiar momentum anisotropy for photoexcited electron-hole pairs. These interband excitations are in fact forbidden along the direction of the light polarization and are maximum perpendicular to it. Here, we use time-and angle-resolved photoemission spectroscopy to investigate the resulting unconventional hot carrier dynamics, sampling carrier distributions as a function of energy, and in-plane momentum. We first show that the rapidly-established quasithermal electron distribution initially exhibits an azimuth-dependent temperature, consistent with relaxation through collinear electron-electron scattering. Azimuthal thermalization is found to occur only at longer time delays, at a rate that depends on the substrate and the static doping level. Further, we observe pronounced differences in the electron and hole dynamics in n-doped samples. By simulating the Coulomb-and phonon-mediated carrier dynamics we are able to disentangle the influence of excitation fluence, screening, and doping, and develop a microscopic picture of the carrier dynamics in photoexcited graphene. Our results clarify new aspects of hot carrier dynamics that are unique to Dirac materials, with relevance for photocontrol experiments and optoelectronic device applications. DOI: 10.1103/PhysRevB.96.020301The existence of anisotropic photocarrier distributions in graphene was predicted [1,2] and observed in optical pump-probe experiments [3-6], which showed a pronounced difference in the time-dependent optical response for different probe polarizations. The decay of the anisotropy extracted in this manner was attributed to optical phonon emission [2][3][4][5]7,8]. However, a complete picture for these nonequilibrium phenomena can only be obtained by tracking both carrier energy and momentum in the time domain.Here we use time-and angle-resolved photoemission spectroscopy (tr-ARPES) at extreme ultraviolet (XUV) wavelengths to track the temporal evolution of the photoexcited carrier distribution as a function of energy and momentum. We establish a hierarchy of events that redistribute carriers on the Dirac cone, including the formation of a quasithermal state with an azimuth-dependent anisotropic electron temperature, which indicates that primary thermalization occurs through collinear electron-electron scattering. Azimuthal relaxation through phonon emission and noncollinear electron-electron scattering plays a role only at later time delays and is found to be strongly influenced by the substrate and the type of static doping of the graphene layer. Furthermore, the finite doping in our samples breaks the electron-hole symmetry and results in different dynamics for electrons and holes. Microscopic simulations of the anisotropic carrier dynamics indicate that the observed dynamics are due to a subtle interplay between doping that affects the scattering phase space and substrate screening which reduces the influence of electron-electron scattering.* sven.aeschlimann@mpsd.mpg.de † is...

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Upconversion of Infrared Light by Graphitic Microparticles Due to Photoinduced Structural Modification

Sharma,

Bhattarai,

Maharjan

et al. 2024

Advanced Photonics Research

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Recent reports of upconversion and white light emission from graphitic particles warrant an explanation of the physics behind the process. A model is offered, wherein the upconversion is facilitated by photoinduced electronic structure modification allowing for multiphoton processes. As per the prediction of the model, it is experimentally shown that graphite upconverts infrared light centered around 1.31 μm (0.95 eV) to broadband white light centered around 0.85 μm (1.46 eV). The results suggest that upconversion from shortwave infrared (≈3 μm, 0.45 eV) to visible region may be possible. The experiments show that the population dynamics of the electronic states involved in this upconversion process occur in the timescale of milliseconds.

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Ultrafast pseudospin dynamics in graphene

Cited by 55 publications

References 57 publications

Ultrafast Multiphoton Thermionic Photoemission from Graphite

Ultrafast Multiphoton Thermionic Photoemission from Graphite

Ultrafast momentum imaging of pseudospin-flip excitations in graphene

Upconversion of Infrared Light by Graphitic Microparticles Due to Photoinduced Structural Modification

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