Phonon-phonon interactions in photoexcited graphite studied by ultrafast electron diffraction

Harb, Maher; Enquist, Henrik; Jurgilaitis, A.; Tuyakova, Feruza T.; Obraztsov, A. N.; Larsson, Jörgen

doi:10.1103/physrevb.93.104104

Cited by 37 publications

(33 citation statements)

References 27 publications

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“…We define τ 0 , at which E ph,LA is the maximum, as the initial relaxation time, which may be determined from time-resolved diffraction experiments [35,36]. Figure 6 shows τ 0 as a function of E e (t = 0) for various f (ε, t = 0).…”

Section: B Impact Of the Nonequilibrium Distributionmentioning

confidence: 99%

Thermalization in simple metals: Role of electron-phonon and phonon-phonon scattering

Ono¹

2018

Phys. Rev. B

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We study the electron and phonon thermalization in simple metals excited by a laser pulse. The thermalization is investigated numerically by solving the Boltzmann transport equation taking into account all the relevant scattering mechanism: the electron-electron, electron-phonon (e-ph), phonon-electron (ph-e), and phonon-phonon (ph-ph) scatterings. In the initial stage of the relaxation, most of the excitation energy is transferred from the electrons to phonons through the e-ph scattering. This creates hot high-frequency phonons due to the ph-e scatterings, followed by an energy redistribution between phonon subsystems through the ph-ph scatterings. This yields an overshoot of the total longitudinal-acoustic phonon energy at a time, across which a crossover occurs from a nonequilibrium state, where the e-ph and ph-e scatterings frequently occur, to a state, where the ph-ph scattering occurs to reach a thermal equilibrium. This picture is quite different from the scenario of the well-known two-temperature model (2TM). The behavior of the relaxation dynamics is compared with those calculated by several models, including the 2TM, the four-temperature model, and nonequilibrium electron or phonon models. The relationship between the relaxation time and the initial distribution function is also discussed.

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Section: B Impact Of the Nonequilibrium Distributionmentioning

confidence: 99%

Thermalization in simple metals: Role of electron-phonon and phonon-phonon scattering

Ono¹

2018

Phys. Rev. B

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“…The larger value of w 0 leads to the faster relaxation. Since the relaxation time in solids is usually an order of ps [18,20,21], we set w 0 = 6 meV. While the use of a realistic potential [27,28] would reveal the themalization of a specific system, such a work is beyond the scope of the present study.…”

Section: Formulationmentioning

confidence: 99%

Nonequilibrium phonon dynamics beyond the quasiequilibrium approach

Ono

2017

Phys. Rev. B

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The description of nonequilibrium states of solids in a simplified manner is a challenge in the field of ultrafast dynamics. Here, the phonon thermalization in solids through the three-phonon scatterings is investigated by solving the Boltzmann transport equation (BTE). The numerical solution of the BTE shows that the transverse acoustic and longitudinal acoustic (LA) phonon temperatures are not well-defined during the relaxation, indicating the breakdown of the quasiequilibrium approximation. The development of hot and cold phonons and the backward energy flow from low to high energy phonons are observed in the initial and final stage of the relaxation, respectively. A minimal model is presented to relate the latter with the power-law decay of the LA phonon energy.Comment: 10 pages, 12 figure

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“…[16,17], techniques for studying ultrafast structural dynamics have not yet reached the equivalent level of resolution. Recently, the investigation of the time-and momentum-resolved phonon population has been demonstrated with ultrafast x-ray and electron diffraction [18][19][20][21].This work reports a momentum-resolved study of scattering processes and the resulting energy transfer between photoexcited electrons and phonons in thin bulklike films of WSe 2 . Specifically, we probe the in-plane structural dynamics following resonant electronic excitation with a short (50 fs) laser pulse by femtosecond electron diffraction, described in Ref.…”

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confidence: 99%

“…The conservation of total momentum requires a probe electron scattering with a phonon to obey the modified Laue condition k pr − k 0 pr ¼ G hkl þ q, where k pr and k 0 pr are the wave vectors before and after the scattering process, G hkl is a reciprocal lattice vector, and q is the wave vector of a phonon [18]. The intensity in between Bragg peaks therefore contains information on the population of phonons as a function of their wave vector [18][19][20][21]26]. In Fig.…”

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confidence: 99%

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Momentum-Resolved View of Electron-Phonon Coupling in Multilayer WSe2

et al. 2017

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We investigate the interactions of photoexcited carriers with lattice vibrations in thin films of the layered transition metal dichalcogenide (TMDC) WSe 2 . Employing femtosecond electron diffraction with monocrystalline samples and first-principles density functional theory calculations, we obtain a momentumresolved picture of the energy transfer from excited electrons to phonons. The measured momentumdependent phonon population dynamics are compared to first-principles calculations of the phonon linewidth and can be rationalized in terms of electronic phase-space arguments. The relaxation of excited states in the conduction band is dominated by intervalley scattering between Σ valleys and the emission of zone boundary phonons. Transiently, the momentum-dependent electron-phonon coupling leads to a nonthermal phonon distribution, which, on longer time scales, relaxes to a thermal distribution via electron-phonon and phononphonon collisions. Our results constitute a basis for monitoring and predicting out of equilibrium electrical and thermal transport properties for nanoscale applications of TMDCs. DOI: 10.1103/PhysRevLett.119.036803 Semiconducting transition metal dichalcogenides combine crystal structures of chemically stable twodimensional layers with indirect band gaps in the visible and near infrared optical range. Their intrinsic stability down to monolayer thicknesses [1,2] in combination with the possibility to create artificial stacks [3,4] suggests them for electronic and optoelectronic applications like nanoscale transistors or photodetectors with atomically sharp p-n junctions [5][6][7]. In such devices, the electronic mobilities, electronic coupling, and heat conductivities within the layers and across interfaces are of central interest. Whereas macroscopic heat and electrical transport properties can be measured directly, the observation of the underlying microscopic processes, i.e., the scattering processes of carriers and of phonons, requires methods with time, momentum, and energy resolution to be understood in detail. Such information can be decisive in the correct determination of transport properties [8,9] or energy relaxation [10][11][12]. A momentum-resolved view of scattering processes will in addition be of uttermost importance in conceiving novel quantum technologies harnessing spin and valley degrees of freedom [13][14][15], as they utilize carrier populations at specific positions in momentum space. While time-and angle-resolved photoemission spectroscopy provides this level of detail for electron dynamics, see, for instance, Refs. [16,17], techniques for studying ultrafast structural dynamics have not yet reached the equivalent level of resolution. Recently, the investigation of the time-and momentum-resolved phonon population has been demonstrated with ultrafast x-ray and electron diffraction [18][19][20][21].This work reports a momentum-resolved study of scattering processes and the resulting energy transfer between photoexcited electrons and phonons in thin bulklike films of WS...

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Phonon-phonon interactions in photoexcited graphite studied by ultrafast electron diffraction

Cited by 37 publications

References 27 publications

Thermalization in simple metals: Role of electron-phonon and phonon-phonon scattering

Thermalization in simple metals: Role of electron-phonon and phonon-phonon scattering

Nonequilibrium phonon dynamics beyond the quasiequilibrium approach

Momentum-Resolved View of Electron-Phonon Coupling in Multilayer WSe2

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