Ultrafast Bond Softening in Bismuth: Mapping a Solid's Interatomic Potential with X-rays

Fritz, David; Reis, David A.; Adams, Bernhard W.; Akre, R.; Arthur, John R.; Blome, C.; Bucksbaum, P. H.; Cavalieri, Adrian L.; Engemann, S.; Fahy, Stephen; Falcone, R. W.; Fuoss, P. H.; Gaffney, Kelly J.; George, Martin J.; Hajdu, János; Hertlein, M. P.; Hillyard, Patrick; Hoegen, M. Horn‐von; Kammler, M.; Kaspar, J.; Kienberger, Reinhard; Krejcik, P.; Lee, S. H.; Lindenberg, A. M.; McFarland, B. K.; Meyer, D.; Montagne, T.; Murray, Éamonn; Nelson, A. J.; Nicoul, M.; Pahl, R.; Rudati, J.; Schlarb, H.; Siddons, D. P.; Sokolowski‐Tinten, K.; Tschentscher, Th.; Linde, D. von der; Hastings, J. B.

doi:10.1126/science.1135009

Cited by 372 publications

(303 citation statements)

References 23 publications

(34 reference statements)

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“…This is a displacive excitation and occurs in a sub-picosecond time scale. [2][3][4] A shear structural deformation of the unit cell is necessary to complete the transition, whose time scale is determined by the excitation of acoustic phonons via anharmonic decay of optical phonons; at room temperature it occurs in 12 ps. 5 These changes are expressed in the following rate equations model: k is the rate constant for the ' α β  transition mediated by the shear distortion; and th k is the rate constant for reaching the thermal equilibrium.…”

Section: Rate Equations Modelmentioning

confidence: 99%

Transient Structures and Possible Limits of Data Recording in Phase-Change Materials

Vanacore

Yang

et al. 2015

ACS Nano

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Phase-change materials (PCMs) represent the leading candidates for universal data storage devices, which exploit the large difference in the physical properties of their transitional lattice structures. On a nanoscale, it is fundamental to determine their performance, which is ultimately controlled by the speed limit of transformation among the different structures involved. Here, we report observation with atomic-scale resolution of transient structures of nanofilms of crystalline germanium telluride, a prototypical PCM, using ultrafast electron crystallography. A nonthermal transformation from the initial rhombohedral phase to the cubic structure was found to occur in 12 ps. On a much longer time scale, hundreds of picoseconds, equilibrium heating of the nanofilm is reached, driving the system toward amorphization, provided that high excitation energy is invoked.These results elucidate the elementary steps defining the structural pathway in the transformation of crystalline-to-amorphous phase transitions and describe the essential atomic motions involved when driven by an ultrafast excitation. The establishment of the time scales of the different transient structures, as reported here, permits determination of the possible limit of performance, which is crucial for high-speed recording applications of PCMs.

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Section: Rate Equations Modelmentioning

confidence: 99%

Transient Structures and Possible Limits of Data Recording in Phase-Change Materials

Vanacore

Yang

et al. 2015

ACS Nano

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“…Recently there has been considerable interest in the dynamics of the A 1g mode in the limit of a dense electronhole plasma, particularly for bismuth [21][22][23][24][25][26][27][28][29] . Hase et al 24 observed that the frequency of the mode is impulsively softened and chirped toward the equilibrium value over a few picoseconds.…”

Section: Introductionmentioning

confidence: 99%

Free-carrier relaxation and lattice heating in photoexcited bismuth

et al. 2013

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We report ultrafast surface pump and interface probe experiments on photoexcited carrier transport across single crystal bismuth films on sapphire. The film thickness is sufficient to separate carrier dynamics from lattice heating and strain, allowing us to investigate the time-scales of momentum relaxation, heat transfer to the lattice and electron-hole recombination. The measured electron-hole (e − h) recombination time is 12-26 ps and ambipolar diffusivity is 18-40 cm 2 /s for carrier excitation up to ∼ 10 19 cm −3 . By comparing the heating of the front and back sides of the film, we put lower limits on the rate of heat transfer to the lattice, and by observing the decay of the plasma at the back of the film, we estimate the timescale of electron-hole recombination. We interpret each of these timescales within a common framework of electron-phonon scattering and find qualitative agreement between the various relaxation times observed. We find that the carrier density is not determined by the e − h plasma temperature after a few picoseconds. The diffusion and recombination become nonlinear with initial excitation > ∼ 10 20 cm −3 .

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“…This motion can be tracked in the time domain by measuring the effects of the coherent phonons on the transient reflectivity of a material and has been used extensively as a probe to study the lattice in near-equilibrium conditions in the vicinity of phase transitions 11 , as well as to look at phonon softening [12][13][14] and hardening 15 when the system is strongly driven. Phonon softening or hardening results from a change in the curvature 16,17 of the lattice potential, but not from a change in the symmetry of the potential. When the symmetry changes, the number of modes typically changes, which may occur when a soft phonon mode tends to zero frequency for a second-order phase transition 14 or may be step-like for a first-order phase transition.…”

mentioning

confidence: 99%

Ultrafast changes in lattice symmetry probed by coherent phonons

et al. 2012

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The electronic and structural properties of a material are strongly determined by its symmetry. Changing the symmetry via a photoinduced phase transition offers new ways to manipulate material properties on ultrafast timescales. However, to identify when and how fast these phase transitions occur, methods that can probe the symmetry change in the time domain are required. Here we show that a time-dependent change in the coherent phonon spectrum can probe a change in symmetry of the lattice potential, thus providing an all-optical probe of structural transitions. We examine the photoinduced structural phase transition in Vo 2 and show that, above the phase transition threshold, photoexcitation completely changes the lattice potential on an ultrafast timescale. The loss of the equilibrium-phase phonon modes occurs promptly, indicating a non-thermal pathway for the photoinduced phase transition, where a strong perturbation to the lattice potential changes its symmetry before ionic rearrangement has occurred.

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Ultrafast Bond Softening in Bismuth: Mapping a Solid's Interatomic Potential with X-rays

Cited by 372 publications

References 23 publications

Transient Structures and Possible Limits of Data Recording in Phase-Change Materials

Transient Structures and Possible Limits of Data Recording in Phase-Change Materials

Free-carrier relaxation and lattice heating in photoexcited bismuth

Ultrafast changes in lattice symmetry probed by coherent phonons

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