Lattice dynamics of oxides with rutile structure and instabilities at the metal-semiconductor phase transitions of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">NbO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">VO</mml:mi></mml:mrow><mml:mrow><

Gervais, F.; Kress, W.

doi:10.1103/physrevb.31.4809

Cited by 134 publications

(77 citation statements)

References 27 publications

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“…We have chosen the parameters as ε c = 1.2 eV, g = 40 and ω 0 = 0.03 eV (Ref. 36) for the independent boson model and G = 1.5 eV 2 and γ = 2 eV for the broadening. Because the tail of the lower binding energy side of the photoemission spectrum reaches the vicinity of E F , we have chosen the coupling constant g so that ε c − ∆ ∼ 0.…”

Section: B Insulating Phasementioning

confidence: 99%

Photoemission study of the metal-insulator transition inVO2/TiO2(001):
Okazaki
¹
,
Wadati
²
,
Fujimori
³

et al. 2004
Phys. Rev. B
107
12
74
0
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We have made a detailed temperature-dependent photoemission study of VO2/TiO2(001) thin films, which show a metal-insulator transition at ∼ 300 K. Clean surfaces were obtained by annealing the films in an oxygen atmosphere. Spectral weight transfer between the coherent and incoherent parts accompanying the metal-insulator transition was clearly observed. We also observed a hysteretic behavior of the spectra for heating-cooling cycles. We have derived the "bulk" spectrum of the metallic phase and found that it has a strong incoherent part. The width of the coherent part is comparable to that given by band-structure calculation in spite of its reduced spectral weight, indicating that the momentum dependence of the self-energy is significant. This is attributed to by ferromagnetic fluctuation arising from Hund's rule coupling between different d orbitals as originally proposed by Zylbersztejn and Mott. In the insulating phase, the width of the V 3d band shows strong temperature dependence. We attribute this to electron-phonon interaction and have reproduced it using the independent boson model with a very large coupling constant.

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Section: B Insulating Phasementioning

confidence: 99%

Photoemission study of the metal-insulator transition inVO2/TiO2(001):
Okazaki
¹
,
Wadati
²
,
Fujimori
³

et al. 2004
Phys. Rev. B
107
12
74
0
View full text Add to dashboard Cite

show abstract

“…The soft mode of the rutile lattice corresponding to this structural transformation is located at the point R = (1/2,0,1/2) of the Brillouin zone. [7][8][9] Correspondingly, the monoclinic phase can be mapped onto the rutile lattice by two normal vibrational modes of vanadium atoms located at the point as a result of the Brillouin zone folding in the monoclinic phase. 10 Working out the exact details of the electronic band structure of VO 2 poses a true challenge to modern manybody theories.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast insulator-metal phase transition in VO2studied by multiterahertz spectroscopy

et al. 2011

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The ultrafast photoinduced insulator-metal transition in VO 2 is studied at different temperatures and excitation fluences using multi-THz probe pulses. The spectrally resolved midinfrared response allows us to trace separately the dynamics of lattice and electronic degrees of freedom with a time resolution of 40 fs. The critical fluence of the optical pump pulse, which drives the system into a long-lived metallic state, is found to increase with decreasing temperature. Under all measurement conditions, we observe a modulation of the eigenfrequencies of the optical phonon modes induced by their anharmonic coupling to the coherent wave-packet motion of V-V dimers at 6.1 THz. Furthermore, we find a weak quadratic coupling of the electronic response to the coherent dimer oscillation resulting in a modulation of the electronic conductivity at twice the frequency of the wave-packet motion. The findings are discussed in the framework of a qualitative model based on an approximation of local photoexcitation of the vanadium dimers from the insulating state.

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“…These modes are associated with pairing and tilting motions of the high-T rutile metal, have been shown by diffuse x-ray scattering experiments to undergo significant softening on crossing T c , 21 and their frequencies have been calculated to be of order 2-4 Thz in the high-T phase. 22 Doubling into the V 4 O 8 low-T unit cell folds these phonons to the center of the Brillouin zone, resulting in A g symmetry and Raman activity. Finally, pairing of the V atoms and electron localization may well stiffen the bonds and result in a 5-6 Thz optical phonon.…”

mentioning

confidence: 99%

Evidence for a structurally-driven insulator-to-metal transition inVO2: A view from the ultrafast timescale

et al. 2004

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We apply ultrafast spectroscopy to establish a time-domain hierarchy between structural and electronic effects in a strongly correlated electron system. We discuss the case of the model system VO 2 , a prototypical nonmagnetic compound that exhibits cell doubling, charge localization, and a metal-insulator transition below 340 K. We initiate the formation of the metallic phase by prompt hole photo-doping into the valence band of the low-T insulator. The insulator-to-metal transition is, however, delayed with respect to hole injection, exhibiting a bottleneck time scale, associated with the phonon connecting the two crystallographic phases. This structural bottleneck is observed despite faster depletion of the d bands and is indicative of important bandlike character for this controversial insulator. Correlated electron materials exhibit remarkable effects, ranging from metal-insulator transitions to nonconventional (high temperature) superconductivity. The subtle interplay between atomic structure, charge, spin, and orbital dynamics is responsible for many of the critical phenomena observed. 1 Importantly, because "simultaneous" changes in more than one degree of freedom are often observed as chemical doping or external parameters are tuned across critical values, time-integrated spectroscopies are unable to uniquely assign cause-effect relationships.Here, we demonstrate that time-resolved spectroscopy can instead be applied to overcome such ambiguities. We study the case of nonmagnetic VO 2 , a controversial, strongly correlated compound that exhibits cell doubling in "concomitance" with electron localization and a metal-insulator transition below 340 K 2 (see Fig. 1). The issue is whether the insulating behavior in the low-T phase derives directly from the Peierls distortion 3 or from electron localization and the consequent increase in electron-electron repulsion. 4,5 Recently, a theoretical study by Wentzcovitch et al. has revived attention into this four-decade-long debate, 6 suggesting that the former mechanism may be dominant, i.e., the low-T phase may be bandlike and the transition structurally driven. New controversy has resulted 7,8 and the problem is yet to be settled experimentally.Previous time-resolved optical 9 and x-ray diffraction 10 experiments in this compound demonstrated that impulsive photoexcitation of the low-T monoclinic insulator causes an ultrafast transition in both the electronic properties and the atomic structural arrangement. However, it was not clear whether the system becomes metallic due to the change in symmetry of the unit cell or to the prompt creation of holes, causing the closure of a Mott gap. We have now performed optical experiments with 15 fs resolution, and we report evidence of a limiting structural time scale for the formation of the metallic phase. This delay is observed despite much faster hole doping into the correlated d band. Such bottleneck time originates from the coherent optical-phonon distortions in the excited state of the system, mapping onto the crystal...

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Lattice dynamics of oxides with rutile structure and instabilities at the metal-semiconductor phase transitions ofNbO2andVO<

Cited by 134 publications

References 27 publications

Photoemission study of the metal-insulator transition inVO2/TiO2(001):
Okazaki
¹
,
Wadati
²
,
Fujimori
³

et al. 2004
Phys. Rev. B
107
12
74
0
View full text Add to dashboard Cite

Photoemission study of the metal-insulator transition inVO2/TiO2(001):
Okazaki
¹
,
Wadati
²
,
Fujimori
³

et al. 2004
Phys. Rev. B
107
12
74
0
View full text Add to dashboard Cite

Ultrafast insulator-metal phase transition in VO2studied by multiterahertz spectroscopy

Evidence for a structurally-driven insulator-to-metal transition inVO2: A view from the ultrafast timescale

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Lattice dynamics of oxides with rutile structure and instabilities at the metal-semiconductor phase transitions ofNbO2andVO<

Cited by 134 publications

References 27 publications

Photoemission study of the metal-insulator transition inVO2/TiO2(001):Okazaki1, Wadati2, Fujimori3 et al. 2004Phys. Rev. B10712740View full textAdd to dashboardCite

Photoemission study of the metal-insulator transition inVO2/TiO2(001):Okazaki1, Wadati2, Fujimori3 et al. 2004Phys. Rev. B10712740View full textAdd to dashboardCite

Ultrafast insulator-metal phase transition in VO2studied by multiterahertz spectroscopy

Evidence for a structurally-driven insulator-to-metal transition inVO2: A view from the ultrafast timescale

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About

Photoemission study of the metal-insulator transition inVO2/TiO2(001):
Okazaki
¹
,
Wadati
²
,
Fujimori
³

et al. 2004
Phys. Rev. B
107
12
74
0
View full text Add to dashboard Cite

Photoemission study of the metal-insulator transition inVO2/TiO2(001):
Okazaki
¹
,
Wadati
²
,
Fujimori
³

et al. 2004
Phys. Rev. B
107
12
74
0
View full text Add to dashboard Cite