Raman scattering in VO2

Schilbe, Peter

doi:10.1016/s0921-4526(02)00584-7

Cited by 223 publications

(154 citation statements)

References 7 publications

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“…Four distinct peaks are observed in the spectrum at 4.4, 5.7, 6.7 and 10.2 THz (147, 191, 224 and 340 cm − 1 ). These frequencies correspond to the four strongest Raman active phonon modes of the M 1 phase that can be coherently excited by our pulse and are in good agreement with those reported in the literature 18 .…”

supporting

confidence: 91%

“…On heating above T c = 343 K, VO 2 becomes metallic and undergoes a first-order structural phase transition to a rutile R-phase with the space group P4 2/mnm , with only two vanadium ions per unit cell. 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.…”

mentioning

confidence: 99%

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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: 91%

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confidence: 99%

Ultrafast changes in lattice symmetry probed by coherent phonons

et al. 2012

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“…3a and shows that, in addition to the two fitted modes, we also observe a low-amplitude oscillation at 10 THz in the data at both wavelengths and an additional peak at 4.3 THz was also observed in most of the 800 nm data sets, but was less reproducible. These additional modes are also A g Raman active modes that are also observed in Raman scattering 20,32 . In principle, these modes can also be used to track the phase transition, however, as their perturbation on the reflectivity is significantly lower than the two modes at 5.6 and 6.7 THz, they will not be discussed further.…”

Section: A Modeling the Dynamicsmentioning

confidence: 76%

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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“…These modes are of A 1g symmetry, and are attributed to twisting of vanadium dimers, with their relative strength depending on the type of insulating phase and crystal orientation with respect to pump and probe polarization 34,38 . Frequencies and linewidths are consistent with corresponding incoherent Raman scattering and track the different insulating phases, of M1, M2 and triclinic with their characteristic frequencies.…”

Section: Discussionmentioning

confidence: 99%

Inhomogeneity of the ultrafast insulator-to-metal transition dynamics of VO2

et al. 2015

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The insulator-metal transition (IMT) of vanadium dioxide (VO 2 ) has remained a longstanding challenge in correlated electron physics since its discovery five decades ago. Most interpretations of experimental observations have implicitly assumed a homogeneous material response. Here we reveal inhomogeneous behaviour of even individual VO 2 microcrystals using pump-probe microscopy and nanoimaging. The timescales of the ultrafast IMT vary from 40±8 fs, that is, shorter than a suggested phonon bottleneck, to 200±20 fs, uncorrelated with crystal size, transition temperature and initial insulating structural phase, with average value similar to results from polycrystalline thin-film studies. In combination with the observed sensitive variations in the thermal nanodomain IMT behaviour, this suggests that the IMT is highly susceptible to local changes in, for example, doping, defects and strain. Our results suggest an electronic mechanism dominating the photoinduced IMT, but also highlight the difficulty to deduce microscopic mechanisms when the true intrinsic material response is yet unclear.

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Raman scattering in VO2

Cited by 223 publications

References 7 publications

Ultrafast changes in lattice symmetry probed by coherent phonons

Ultrafast changes in lattice symmetry probed by coherent phonons

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

Inhomogeneity of the ultrafast insulator-to-metal transition dynamics of VO2

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