Ultrafast structural phenomena: theory of phonon frequency changes and simulations with code for highly excited valence electron systems

Grigoryan, Naira S.; Zier, Tobias; Garcia, Martín E.; Zijlstra, Eeuwe S.

doi:10.1364/josab.31.000c22

Cited by 21 publications

(10 citation statements)

References 25 publications

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“…The charge distribution is direction dependent due to breaking symmetry and is much pronounced in the plane perpendicular to the pulse direction. Two scenarios are available for laser-induced phonon frequency changes according to N. S. Grigoryan et al [43]. If atomic movement occurs in the direction of a phonon mode and leads to growing the electronic density of states at Fermi state, then irradiation of laser would decrease the potential energy surface PES.…”

Section: Resultsmentioning

confidence: 99%

Transient non-linear optics of diamond under ultrashort excitation pulses

2021

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Electronic response of crystalline diamond as well as high harmonic generation following irradiation by a single-cycle highintensity laser pulse was calculated through modeling the dynamics in the framework of the time-dependent density functional theory. The frequencies of the applied laser pulses vary over visible regime with a timescale shorter than typical quantum dephasing. High harmonic yields, show substantial deviation from what is obtained from the power scaling law of perfect solids under longer cycle pulses due to the key role of strong nonlinear features of dynamics at high intensities. Further, the dynamical photon dressing of electronic states are monitored by Floquet quasi-static picture for ultrashort few cycle pulses. Our results show that dynamical bandgap is diminished as a function of increasing driven field frequency and the system changes into the dynamic metallization regimes that consequently leads to new hybridization of quasi static dressed bands particularly near high symmetrical points in the Brillouin zone. These Floquet hybridization can be used to produce coherent transport of charge on the scale of the huge number of lattice sites. Moreover, the pulse-induced phonon frequency variations that relate to bond softening and hardening, are connected to different order of Floquet dressed states. Importantly, it is found that dielectric response oscillation is directly proportional to the transient bandgap value so that entering into metallization mode preserves the polarization coherency. Based on the magnitude of calculated Keldysh parameter varies for dynamical bandgap, tunneling ionization is the dominant mechanism of excitation.

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Section: Resultsmentioning

confidence: 99%

Transient non-linear optics of diamond under ultrashort excitation pulses

2021

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“…Phonon dispersion with quasi-harmonic approximation might not be persuasive, especially for cases far away from equilibrium. Focusing on the crystal instability and phonon hardening [46,51,65,[69][70][71] cases, we plotted the potential energy surface (PES) of Al and Cu in the normal coordinates for the transverse acoustic (TA) and longitudinal acoustic (LA) modes at the high-symmetry point L( 12 , 1 2 , 1 2 ) in the first Brillouin zone to include anharmonicity effect. The scaling factor Q 1 of the lowest TA mode and the scaling factor Q 2 of the LA mode are applied in the calculation, and the PES is a function of scaled coordinates E = E(Q 1 , Q 2 ); we do not show the second-lowest TA mode because it is degenerate with the lowest TA mode.…”

Section: Potential Energy Surfacementioning

confidence: 99%

Effect of Nonequilibrium Transient Electronic Structures on Lattice Stability in Metals: Density Functional Theory Calculations

Zhang

Zeng

et al. 2022

Front. Phys.

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The electronic structures of metals undergo transient nonequilibrium states during the photoexcitation process caused by isochoric heating of X-ray free-electron laser, and their lattice stability is, thus, significantly affected. By going beyond frozen core approximation, we manually introduced nonequilibrium electron distribution function in finite-temperature density functional theory with the framework of Kohn–Sham–Mermin to investigate such transient states, and their effect on lattice stability in metals is demonstrated by phonon dispersion calculated using the finite displacement method. We found that the perfect lattice of a metal collapses due to the exotic electronic structure of nonequilibrium transient state created by isochoric heating of X-ray free-electron laser. Further increase of the number of holes created in the sample (i.e., an increase of laser fluence) still results in lattice instability for aluminum, while for copper, it results in phonon hardening. The potential energy surface is calculated for the extreme case of both Al and Cu with exactly one hole created in its inner shell for each one of the atoms. A double-well structure is clearly observed for Al, while the potential energy surface becomes steeper for Cu.

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“…Our simulations were performed using our in-house Code for Highly excIted Valence Electron Systems (CHIVES), which is two orders of magnitude faster than other state-of-the-art density-functional-theory (DFT) codes for the same accuracy [18,19]. In CHIVES, the equations of motion for the atoms are integrated under the influence of a laser-excited PES, which is computed by solving the electronic problem in the local density approximation [20].…”

Section: A Molecular Dynamics Simulations Of Laser-excited Antimonymentioning

confidence: 99%

Nonequilibrium dynamics of the phonon gas in ultrafast-excited antimony

Krylow

Zijlstra

Kabeer

et al. 2017

Phys. Rev. Materials

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The ultrafast relaxation dynamics of a nonequilibrium phonon gas towards thermal equilibrium involves manybody collisions that cannot be properly described by perturbative approaches. Here, we develop a nonperturbative method to elucidate the microscopic mechanisms underlying the decay of laser-excited coherent phonons in the presence of electron-hole pairs, which so far are not fully understood. Our theory relies on ab initio molecular dynamics simulations on laser-excited potential-energy surfaces. Those simulations are compared with runs in which the laser-excited coherent phonon is artificially deoccupied. We apply this method to antimony and show that the decay of the A 1g phonon mode at low laser fluences can be accounted mainly to three-body down-conversion processes of an A 1g phonon into acoustic phonons. For higher excitation strengths, however, we see a crossover to a four-phonon process, in which two A 1g phonons decay into two optical phonons.

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Ultrafast structural phenomena: theory of phonon frequency changes and simulations with code for highly excited valence electron systems

Cited by 21 publications

References 25 publications

Transient non-linear optics of diamond under ultrashort excitation pulses

Transient non-linear optics of diamond under ultrashort excitation pulses

Effect of Nonequilibrium Transient Electronic Structures on Lattice Stability in Metals: Density Functional Theory Calculations

Nonequilibrium dynamics of the phonon gas in ultrafast-excited antimony

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