Ultrafast anisotropic disordering in graphite driven by intense hard X-ray pulses

Hartley, N. J.; Grenzer, J.; Lu, Wei; Huang, Lingen; Inubushi, Yuichi; Kamimura, N.; Katagiri, Kento; Kodama, R.; Kon, Akira; Lipp, Vladimir; Makita, Mikako; Matsuoka, Takeshi; Medvedev, Nikita; Nakajima, S.; Ozaki, Norimasa; Pikuz, T. A.; Rode, Andrei; Rohatsch, K.; Sagae, Daisuke; Schuster, A. K.; Tono, Kensuke; Vorberger, Jan; Yabuuchi, T.; Kraus, D.

doi:10.1016/j.hedp.2019.05.002

Cited by 15 publications

(10 citation statements)

References 46 publications

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“…Shortly after that, thermal melting of the new phase starts. However, at modern X-ray free-electron laser facilities, equipped for femtosecond time-resolved diffraction experimental capabilities, one should be able to observe the nonthermal transitions 61 . Thus, we suggest that X-ray-pump X-ray-probe experiments, homogeneously heating nanoclusters and probing their structure at sub-picosecond scales, should be able to experimentally validate our predictions 62 .…”

Section: Discussionmentioning

confidence: 99%

Nonthermal phase transitions in metals

Medvedev

Milov

2020

Sci Rep

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It is well known that sufficiently thick metals irradiated with ultrafast laser pulses exhibit phonon hardening, in contrast to ultrafast nonthermal melting in covalently bonded materials. It is still an open question how finite size metals react to irradiation. We show theoretically that generally metals, under high electronic excitation, undergo nonthermal phase transitions if material expansion is allowed (e.g. in finite samples). The nonthermal phase transitions are induced via an increase of the electronic pressure which leads to metal expansion. This, in turn, destabilizes the lattice triggering a phase transition without a thermal electron-ion coupling mechanism involved. We find that hexagonal close-packed metals exhibit a diffusionless transition into a cubic phase, whereas metals with a cubic lattice melt. In contrast to covalent solids, nonthermal phase transitions in metals are not ultrafast, predicative on the lattice expansion. Ultrafast deposition of high energy density into a solid target creates far-from-equilibrium states of matter with unusual properties that are not achievable in equilibrium states 1-3. Such a material with dynamically changing properties poses fundamental difficulties for a theoretical description, as it occupies the gap in standard methods between the solid state, plasma, chemical physics, and other disciplines 4,5. Such energy deposition may be realized via irradiation of the target with intense femtosecond laser pulses, in particular from X-ray free-electron lasers (XFEL) such as e.g. LCLS 6 , SACLA 7 , EuXFEL 8 , etc. In an irradiated solid, energy deposition by photons excites primarily the electronic system 9. Excited electrons transfer their energy to the ions, which may result in material modifications 10. Upon ultrafast energy deposition into an electronic system of a material, there are two typical scenarios of material damage. Energy transfer via electronphonon (or, more generally, electron-ion) coupling leads to heating of the atomic system, which, when exceeding the melting threshold, leads to atomic disordering. Alternatively, electronic excitation may affect the interatomic potential and destabilize the lattice without any electron-ion coupling involved. Such a mechanism is known as nonthermal melting, and has been demonstrated to take place in highly excited covalently bonded materials 1,11,12. Since the original work by Recoules et al. 13 , it is generally accepted in the laser-mater interaction community that metals do not melt nonthermally. Indeed, it was shown that bulk metals typically exhibit hardening of phonon modes under intense electronic excitation, in contrast to covalently bonded materials 12-14 , materials with mixed ionic-covalent bonds 15,16 , or with Peierls distortions 17. Absence of nonthermal melting in metals was confirmed in numerous subsequent ab-initio simulations for various metals, see e.g. Ref. 18. Experimental evidence supported this conclusion 19,20. On the other hand, softening of phonon modes in gold nanospheres was reported in R...

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Section: Discussionmentioning

confidence: 99%

Nonthermal phase transitions in metals

Medvedev

Milov

2020

Sci Rep

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“…In particular, the way that NLTE dynamics simulations are fed by LTE IPD input such as EK and SP might be questionable for calculation of XFEL-created dense plasmas. Furthermore, nonthermal femtosecond phase transitions induced by an intense hard-x-ray pulse have been reported [51,52], thus necessitating an IPD treatment that is unrestricted, for both electrons and ions, by any thermal equilibrium condition.…”

Section: Introductionmentioning

confidence: 99%

Transient ionization potential depression in nonthermal dense plasmas at high x-ray intensity

et al. 2021

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The advent of x-ray free-electron lasers (XFELs), which provide intense ultrashort x-ray pulses, has brought a new way of creating and analyzing hot and warm dense plasmas in the laboratory. Because of the ultrashort pulse duration, the XFEL-produced plasma will be out of equilibrium at the beginning, and even the electronic subsystem may not reach thermal equilibrium while interacting with a femtosecond timescale pulse. In the dense plasma, the ionization potential depression (IPD) induced by the plasma environment plays a crucial role for understanding and modeling microscopic dynamical processes. However, all theoretical approaches for IPD have been based on local thermal equilibrium (LTE), and it has been controversial to use LTE IPD models for the nonthermal situation. In this work, we propose a non-LTE (NLTE) approach to calculate the IPD effect by combining a quantum-mechanical electronic-structure calculation and a classical molecular dynamics simulation. This hybrid approach enables us to investigate the time evolution of ionization potentials and IPDs during and after the interaction with XFEL pulses, without the limitation of the LTE assumption. In our NLTE approach, the transient IPD values are presented as distributions evolving with time, which cannot be captured by conventional LTE-based models. The time-integrated ionization potential values are in good agreement with benchmark experimental data on solid-density aluminum plasma and other theoretical predictions based on LTE. The present work is promising to provide critical insights into nonequilibrium dynamics of dense plasma formation and thermalization induced by XFEL pulses.

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“…To date, X-ray measurements of ultrafast melting or disordering have largely relied on changes in diffraction peaks, as in previous work at SACLA [9,10] and elsewhere [11]. The latter, by Pardini et al, demonstrates the challenges of studying phase transitions by observing weakening of diffraction lines, particularly when both the pump and probe pulse are at the same energy; what was initially believed to be strong diffraction signal from silicon 333 up to 150 fs after X-ray heating was in fact due to fluctuations in the pulse fluences and a loss of beam overlap [11,12].…”

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confidence: 99%

Using Diffuse Scattering to Observe X-Ray-Driven Nonthermal Melting

Hartley,

Grenzer,

Huang

et al. 2020

Preprint

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We present results from the SPring-8 Angstrom Compact free electron LAser (SACLA) XFEL facility, using a high intensity (∼ 10 20 W/cm 2 ) X-ray pump X-ray probe scheme to observe changes in the ionic structure of silicon induced by X-ray heating of the electrons. By avoiding Laue spots in the scattering signal from a single crystalline sample, we observe a rapid rise in diffuse scattering, which we attribute to a loss of lattice order and a transition to a liquid state within 100 fs of irradiation, a timescale which agrees well with first principles simulations, but is faster than that predicted by purely inertial behavior. This method is capable of observing liquid scattering without masking or filtering of signal from the ambient solid, allowing the liquid structure to be measured throughout and beyond the phase change.

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Ultrafast anisotropic disordering in graphite driven by intense hard X-ray pulses

Cited by 15 publications

References 46 publications

Nonthermal phase transitions in metals

Nonthermal phase transitions in metals

Transient ionization potential depression in nonthermal dense plasmas at high x-ray intensity

Using Diffuse Scattering to Observe X-Ray-Driven Nonthermal Melting

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