Optical induction and detection of fast phase transition in VO2

Roach, W. R.; Balberg, I.

doi:10.1016/0038-1098(71)90144-x

Cited by 46 publications

(29 citation statements)

References 9 publications

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“…The increased symmetry reduces the number of Raman active phonon modes from 18 in the M 1 phase to 4 in the R-phase, without any significant mode softening near the transition temperature 18 . The same structural transition has been induced on the ultrafast timescale by exciting M 1 -phase VO 2 at room temperature with an intense 800 nm pump laser, using a pump fluence greater than F th~7 mJ cm − 2 , and observed by femtosecond X-ray 6,19 and electron diffraction 7 , as well as through changes in the optical 20,21 and electrical 22,23 properties. These experiments show that the complete transformation to the R-phase, after some initial fast dynamics, is a slow process, taking hundreds of picoseconds to complete.…”

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confidence: 71%

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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confidence: 71%

Ultrafast changes in lattice symmetry probed by coherent phonons

et al. 2012

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“…Dynamically, via photoexcitation above the bandgap, 4 the structural phase transition has been resolved on the atomic spatiotemporal scale to proceed along a stepwise reaction path, where the atoms move from the initial over transitional to final conformations with a hierarchy of time scales ranging from femtoseconds (fs) to hundreds of picoseconds (ps) 5 . Different aspects of this path require different degrees of cooperation, evident from the distinct energy thresholds below which the structural phase transition does not fully proceed 5,6 .…”

Section: Introductionmentioning

confidence: 99%

Ultrafast electron crystallography of the cooperative reaction path in vanadium dioxide

Yang

Baum

Zewail

2016

Structural Dynamics

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Time-resolved electron diffraction with atomic-scale spatial and temporal resolution was used to unravel the transformation pathway in the photoinduced structural phase transition of vanadium dioxide. Results from bulk crystals and single-crystalline thin-films reveal a common, stepwise mechanism: First, there is a femtosecond V−V bond dilation within 300 fs, second, an intracell adjustment in picoseconds and, third, a nanoscale shear motion within tens of picoseconds. Experiments at different ambient temperatures and pump laser fluences reveal a temperature-dependent excitation threshold required to trigger the transitional reaction path of the atomic motions.

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“…However, very recent calculations have shown that, when non-local exchange interactions are accounted for, the insulating and metallic phases can be obtained within DFT and additional correlation effects are not required 4,5 . The discovery of a photoinduced IM transition in VO 2 has opened new avenues for investigating the transition process 6 . In these time-resolved experiments, a strong pump pulse excites the system and a second pulse probes a specific property as a function of time delay.…”

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confidence: 99%

Tracking the evolution of electronic and structural properties of VO2during the ultrafast photoinduced insulator-metal transition

et al. 2013

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We present a detailed study of the photoinduced insulator-metal transition in VO2 with broadband time-resolved reflection spectroscopy. This allows us to separate the response of the lattice vibrations from the electronic dynamics and observe their individual evolution. When exciting well above the photoinduced phase transition threshold, we find that the restoring forces that describe the ground state monoclinic structure are lost during the excitation process, suggesting that an ultrafast change in lattice potential drives the structural transition. However, by performing a series of pump-probe measurements during the non-equilibrium transition, we observe that the electronic properties of the material evolve on a different, slower, timescale. This separation of timescales suggests that the early state of VO2, immediately after photoexcitation, is a non-equilibrium state that is not well defined by either the insulating or metallic phase.

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Optical induction and detection of fast phase transition in VO2

Cited by 46 publications

References 9 publications

Ultrafast changes in lattice symmetry probed by coherent phonons

Ultrafast changes in lattice symmetry probed by coherent phonons

Ultrafast electron crystallography of the cooperative reaction path in vanadium dioxide

Tracking the evolution of electronic and structural properties of VO2during the ultrafast photoinduced insulator-metal transition

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