First-Principles Calculation of Femtosecond Symmetry-Breaking Atomic Forces in Photoexcited Bismuth

Murray, Éamonn; Fahy, Stephen

doi:10.1103/physrevlett.114.055502

Cited by 17 publications

(19 citation statements)

References 29 publications

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“…an excitation of the E g optical phonon mode, can in principle occur by stimulated Raman-scattering [43] and, for stronger excitation, via anharmonic coupling to the displacively excited A g 1 mode (motion along the c-axis) [44]. Time-resolved x-ray diffraction measurements [45] have however shown, that the coherent excitation of the E g -mode is weak and strongly damped, which has been explained by the very short lifetime of the electronic states driving the mode [46,47]. Therefore, the diffraction data can be used to determine Dá ñ u 2 as a function of delay time.…”

Section: Transient Debye-waller Effectmentioning

confidence: 99%

Thickness-dependent electron–lattice equilibration in laser-excited thin bismuth films

Sokolowski‐Tinten

Reid

et al. 2015

New J. Phys.

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Section: Transient Debye-waller Effectmentioning

confidence: 99%

Thickness-dependent electron–lattice equilibration in laser-excited thin bismuth films

Sokolowski‐Tinten

Reid

et al. 2015

New J. Phys.

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“…Previous theoretical work on coherent phonon motion in bismuth has concentrated largely on the coupling of electronic photo-excitation with the zone center A 1g and E g modes, [17,18,24] with some other calculations of the softening effects of photoexcitation on modes throughout the Brillouin zone [19]. In this paper we address the anharmonic coupling of the A 1g mode to modes with wave vectors throughout the Brillouin zone.…”

mentioning

confidence: 99%

“…The material is a simple, classic semimetal, which in principle allows one to study energy relaxation processes and induced atomic dynamics in a material intermediate between semiconductors and metals [10,15,18,23,24]. The A 1g atomic motion in photoexcited bismuth [16,25,26] has been measured recently using time-resolved Bragg scattering.…”

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confidence: 99%

Resonant squeezing and the anharmonic decay of coherent phonons

2016

Self Cite

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We show that the anharmonic decay of large-amplitude coherent phonons in a solid generates strongly enhanced squeezing of the phonon modes near points of the Brillouin zone where energy conservation in the three-phonon decay process is satisfied. The squeezing process leads to temporal oscillations of the mean-square displacement of target modes in resonance with the coherent phonon, which are characteristic of coherent phonon decay and do not occur in the decay of a phonon in a well-defined number state. For realistic material parameters of optically excited group-V semimetals, we predict that this squeezing results in strongly enhanced oscillations of the x-ray diffuse scattering intensity at sharply-defined values of the x-ray momentum transfer. Numerical simulations of the phonon dynamics and x-ray diffuse scattering in optically-excited bismuth, using harmonic and anharmonic force parameters calculated with constrained density functional theory, demonstrate oscillations of the diffuse scattering intensity of magnitude 10-20% of the thermal background at points of the Brillouin zone, where resonance occurs. Such oscillations should be observable using time-resolved optical-pump/x-ray-probe facilities available at current x-ray free-electron laser sources.PACS numbers: 63.20.kg, 63.20.dk, 78.70.Ck The effect of mode coupling in strongly anharmonic materials has long been of interest, with important consequences for thermal transport and thermalization of energy within the vibrational modes [1]. The anharmonic decay of vibrational modes has been qualitatively understood in terms of quantum perturbation theory for many decades [2] and in more recent times, accurate quantitative calculations of phonon decay rates, based on density functional theory, have been possible [3]. It has been pointed out [4] that higher-order correlations of the phonon modes during the quantum decay process of a coherent phonon at very low temperature could in principle create squeezed quantum states, although substantial difficulties were envisaged in the detection of such squeezed states.We show in this paper that significant non-trivial correlated dynamics occur in the target modes (decay products) at high temperature during anharmonic decay of a coherent phonon -in particular, the target modes of the decay process exhibit squeezed phonon dynamics in this regime, generated in a process analogous to classical parametric resonance [5]. From simulations of the decay of the photo-excited coherent A 1g mode in bismuth, we show that such resonant squeezing of modes causes oscillations of the x-ray diffuse scattering in some regions of the Brillouin zone, which are of the order of 10-20% of the room-temperature diffuse thermal background, and should be directly observable using time-resolved x-ray diffuse scattering [6]. Although mode squeezing is often viewed as a primarily quantum phenomenon [7,8], this effect is by no means confined to the quantum regime [9] and we suggest a broader physical regime of phonon motion, in which squeezing...

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“…With respect to the DECP mechanism, instead, the anisotropic phonon behavior may be explained by anisotropy in the electron-phonon interaction, especially when it occurs immediately after photo-excitation. As theoretically predicted13, the distribution of photo-induced carriers, which is strongly governed by the direction of the applied electric field, determines the direction of the displacement of the lattice82728. Indeed, the intensity of the Raman signal is very small in Ge-Sb-Te materials29 and this result implies that the Raman cross section in Ge-Sb-Te materials is not large enough for the Raman process to be the dominant generation mechanism.…”

Section: Discussionmentioning

confidence: 90%

“…In opaque materials, coherent optical phonons can be driven by three well-known mechanisms, namely, impulsive stimulated Raman scattering (ISRS)910, displacive excitation of coherent phonons (DECP)11, and ultrafast screening of the space-charge (SC) field12. Recent theoretical studies have succeeded in the computational treatment of not only the isotropic but also the anisotropic contribution to the photo-induced driving force of coherent phonons and have revealed new quantitative insights about the optical response of the lattice13. These results suggest that excitation of anisotropic carrier distributions can drive coherent atomic motion beyond the framework of Raman scattering.…”

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confidence: 99%

Anisotropic lattice response induced by a linearly-polarized femtosecond optical pulse excitation in interfacial phase change memory material

Makino

Saito

Fons

et al. 2016

Sci Rep

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Optical excitation of matter with linearly-polarized femtosecond pulses creates a transient non-equilibrium lattice displacement along a certain direction. Here, the pump and probe pulse polarization dependence of the photo-induced ultrafast lattice dynamics in (GeTe)2/(Sb2Te3)4 interfacial phase change memory material is investigated under obliquely incident conditions. Drastic pump polarization dependence of the coherent phonon amplitude is observed when the probe polarization angle is parallel to the c–axis of the sample, while the pump polarization dependence is negligible when the probe polarization angle is perpendicular to the c–axis. The enhancement of phonon oscillation amplitude due to pump polarization rotation for a specific probe polarization angle is only found in the early time stage (≤2 ps). These results indicate that the origin of the pump and probe polarization dependence is dominantly attributable to the anisotropically-formed photo-excited carriers which cause the directional lattice dynamics.

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First-Principles Calculation of Femtosecond Symmetry-Breaking Atomic Forces in Photoexcited Bismuth

Abstract: Type of publicationArticle (peer-reviewed) Access to the full text of the published version may require a subscription. Rights

Cited by 17 publications

References 29 publications

Thickness-dependent electron–lattice equilibration in laser-excited thin bismuth films

Thickness-dependent electron–lattice equilibration in laser-excited thin bismuth films

Resonant squeezing and the anharmonic decay of coherent phonons

Anisotropic lattice response induced by a linearly-polarized femtosecond optical pulse excitation in interfacial phase change memory material

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