Modeling of material properties after ultrashort laser and XUV excitation

Zijlstra, Eeuwe S.; Kabeer, Fairoja Cheenicode; Bauerhenne, Bernd; Zier, Tobias; Grigoryan, Naira S.; Garcia, Martín E.

doi:10.1007/s00339-012-7183-0

Cited by 18 publications

(14 citation statements)

References 37 publications

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“…In contrast, the phonon frequencies in Al and TiO 2 have been reported to change only little or not at all [29,33]. Moreover, in Mg we have predicted that upon laser excitation the transverse acoustic parallel mode at the M point softens [31]. In this paper we report that the transverse optical parallel (TO ) phonon mode at the K point in the Brillouin zone even reveals both softening and hardening as a function of the absorbed laser energy.…”

Section: Introductionmentioning

confidence: 72%

“…In semiconductors and semimetals, the hot carriers typically induce bond softening [14,28,29] due to the excitation of electrons from bonding to antibonding states. In metals, phonons have been found to harden [29][30][31][32] upon femtosecond-laser excitation. In contrast, the phonon frequencies in Al and TiO 2 have been reported to change only little or not at all [29,33].…”

Section: Introductionmentioning

confidence: 99%

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Electronic origin of bond softening and hardening in femtosecond-laser-excited magnesium

2014

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Many ultrafast structural phenomena in solids at high fluences are related to the hardening or softening of particular lattice vibrations at lower fluences. In this paper we relate femtosecond-laser-induced phonon frequency changes to changes in the electronic density of states, which need to be evaluated only in the electronic ground state, following phonon displacement patterns. We illustrate this relationship for a particular lattice vibration of magnesium, for which we-surprisingly-find that there is both softening and hardening as a function of the femtosecond-laser fluence. Using our theory, we explain these behaviours as arising from Van Hove singularities: We show that at low excitation densities Van Hove singularities near the Fermi level dominate the change of the phonon frequency while at higher excitations Van Hove singularities that are further away in energy also become important. We expect that our theory can as well shed light on the effects of laser excitation of other materials.

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Section: Introductionmentioning

confidence: 72%

Section: Introductionmentioning

confidence: 99%

Electronic origin of bond softening and hardening in femtosecond-laser-excited magnesium

2014

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“…Recent theoretical [23] and experimental [24] studies on noble metals predict a hardening of phonon modes after electronic excitation on extremely short time scales, i.e., shorter than the equilibration between the excited electrons and the lattice, which lasts picoseconds [25]. Figure 1 shows this effect for the longitudinal L-and X-point phonons in silver.…”

Section: Origin Of Bond Hardeningmentioning

confidence: 91%

“…1. In contrast to semimetals, Ag shows bond hardening after ultrashort-laser excitation [23] (Sec. II), but its influence (Sec.…”

Section: Introductionmentioning

confidence: 99%

Transient phonon vacuum squeezing due to femtosecond-laser-induced bond hardening

et al. 2014

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Ultrashort optical pulses can be used both to create fundamental quasiparticles in crystals and to change their properties. In noble metals, femtosecond lasers induce bond hardening, but little is known about its origin and consequences. Here we simulate ultrafast laser excitation of silver at high fluences. We compute laser-excited potential-energy surfaces by all-electron ab initio theory and analyze the resulting quantum lattice dynamics. We also consider incoherent lattice heating due to electron-phonon interactions using the generalized two-temperature model. We find phonon hardening, which we attribute to the excitation of s electrons. We demonstrate that this may result in phonon vacuum squeezed states with an optimal squeezing factor of ∼0.001 at the L-point longitudinal mode. This finding implies that ultrafast laser-induced bond hardening may be used as a tool to manipulate the quantum state of opaque materials, where, so far, the squeezing of phonons below the zero-point motion has only been realized in transparent crystals by a different mechanism. On the basis of our finding, we further propose a method for directly measuring bond hardening.

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“…This electron is added to the conduction band in order to maintain charge neutrality. [22,23] In Figure 1, which shows part of our supercell, the thus excited atom has been colored red. One of the nearest neighbors is then displaced along the line connecting it with the excited atom, as indicated by a purple arrow.…”

mentioning

confidence: 99%

Melting of Al Induced by Laser Excitation of 2p Holes

Rosandi

Kabeer

Cherednikov

et al. 2015

Materials Research Letters

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Novel photon sources—such as XUV- or X-ray lasers—allow to selectively excite core excitations in materials. We study the response of a simple metal, Al, to the excitation of 2p holes using molecular dynamics simulations. During the lifetime of the holes, the interatomic interactions in the slab are changed; we calculate these using WIEN2k. We find that the melting dynamics after core-hole excitation is dominated by classical electron–phonon dynamics. The effects of the changed potential surface for excited Al atoms occur on the time scale of 100 fs, corresponding to the Debye time of the lattice

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Modeling of material properties after ultrashort laser and XUV excitation

Cited by 18 publications

References 37 publications

Electronic origin of bond softening and hardening in femtosecond-laser-excited magnesium

Electronic origin of bond softening and hardening in femtosecond-laser-excited magnesium

Transient phonon vacuum squeezing due to femtosecond-laser-induced bond hardening

Melting of Al Induced by Laser Excitation of 2p Holes

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