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Okazaki, Kozo; Wadati, H.; Fujimori, A.; Onoda, Mitsuko; Muraoka, Yuji; Hiroi, Zenji

doi:10.1103/physrevb.69.165104

Cited by 107 publications

(88 citation statements)

References 36 publications

(49 reference statements)

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“…The theoretical result is compared with the raw data without subtraction of the O-2p and surface contribution. Subtraction of the surface contribution as in [11] would lead to even better agreement, as explained in the text.…”

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confidence: 87%

“…Additional subtraction due to surface contributions to the incoherent part [11] results in noticeably more spectral weight at low energy compared to that at −1.5 eV .…”

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confidence: 99%

“…Comparison of theoretical (LDA +DMFT) result for the total one-electron spectral function in the metallic phase of V O2 to the experimental results taken from [11] (for PES) and from [9] (for XAS). The inset shows a blow-up of the PES spectrum.…”

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confidence: 99%

“…One-electron spectroscopies constitute a reliable fingerprint of the changes in the single-particle spectral Photoemission spectrum of V O2 across the metal-insulator transition, from [11]. Top: raw data; bottom: with the O-2p background subtracted in a way indicated by the region below the solid (300 K) and dashed (350 K) lines.…”

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confidence: 99%

“…Usually, the experiments have been carried out with low incident photon energies (50 − 70 eV) except in Ref. [11] (1200 eV). However, the main features, namely: (i) a broad step-like feature crossing E F in the R phase, (ii) the "lower Hubbard band" centered at −1 eV, and (iii) the huge O 2p-band contribution from −2 eV, seem to be roughly consistent in all these measurements.…”

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confidence: 99%

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VO ₂ : A two-fluid incoherent metal?

2005

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We present ab initio LDA+DMFT results for the many-particle density of states of V O2 on the metallic side of the strongly first-order (T -driven) insulator-metal transition. In strong contrast to LDA predictions, there is no remnant of even correlated Fermi liquid behavior in the correlated metal. Excellent quantitative agreement with published photoemission and X-ray absorption experiments is found in the metallic phase. We argue that the absence of FL-quasiparticles provides a natural explanation for the bad-metallic transport for T > 340 K. Based on this agreement, we propose that the I-M transition in V O2 is an orbital-selective Mott transition, and point out the relevance of orbital resolved one-electron and optical spectroscopy to resolve this outstanding issue. A detailed understanding of the above cases is still somewhat elusive. In particular, it is still unclear whether the MIT is orbital selective, i.e., whether different orbital-resolved densities-of-states (DOS) are gapped (driving the Mott insulating state) at different values of U, U ′ (defined below) or whether there is a single (common) Mott transition at a critical interaction strength [3,4]. Conflicting results, even for the same system, and within the same (d = ∞) approximation [4] have been obtained, necessitating more work to resolve this issue.In this communication, we address precisely this issue in vanadium dioxide (V O 2 ). Using the state-of-the-art LDA+DMFT [5] technique, we first show how excellent quantitative agreement with the full, local one-electron spectral function is achieved using LDA+DMFT(IPT). We then build on this agreement, claiming that the MIT in V O 2 is orbital selective, and represents a concrete, ab initio realization of the two-fluid scenario for MIT in strongly correlated systems.V O 2 shows a spectacular MIT at T = 340 K from a low-T monoclinic, Mott insulating phase with spin dimerization along the crystallographic c-axis to a local moment paramagnetic metallic phase. This T -driven MIT has attracted intense scrutiny: because of the additional complication of the antiferroelectric displacement of the V O 6 octahedra in a correlated system, an unambiguous characterization of the MIT (relative importance of MottHubbard versus Peierls dimerization) is somewhat difficult. Various observations have been cited in support of both scenarios [1], and theoretical models detailing the importance of these effects have been proposed [6,7].One-electron spectroscopies constitute a reliable fingerprint of the changes in the single-particle spectral

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confidence: 87%

“…Additional subtraction due to surface contributions to the incoherent part [11] results in noticeably more spectral weight at low energy compared to that at −1.5 eV .…”

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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VO ₂ : A two-fluid incoherent metal?

2005

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Versatile Tunability of the Metal Insulator Transition in (TiO₂)_m/(VO₂)_m Superlattices

Eres

Lee

Nichols

et al. 2020

Adv Funct Materials

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In contrast to perovskites that share only common corners of cation‐occupied octahedra, binary‐oxides in addition share edges and faces increasing the versatility for tuning the properties and functionality of reduced dimensionality systems of strongly correlated oxides. This approach for tuning the electronic structure is based on the ability of X‐ray spectroscopy methods to monitor the creation and transformation of occupied and unoccupied electronic states produced by interface coupling and lattice distortions. X‐ray diffraction reveals a new range of structural metastability in (TiO2)m/(VO2)m/TiO2(001) superlattices with m = 1, 3, 5, 20, 40, and electrical transport measurements show metal insulator transition (MIT) behavior typically associated with presence of high oxygen vacancy concentrations. However, X‐ray absorption spectroscopy (XAS) at the Ti and V L3,2‐edge and resonant inelastic X‐ray scattering (RIXS) at the Ti and V L3‐edge show no excitations characteristic of oxygen vacancy induced valance change in V and negligible intensities in Ti RIXS. The unexpected absence of oxygen vacancy related states in the X‐ray spectroscopy data suggests that superlattice fabrication is capable of suppressing oxygen vacancy formation while still affording a wide tunability range of the MIT. Achieving a wide range of MIT tunability while reducing or eliminating oxygen vacancies that are detrimental to electrical properties is highly desirable for technological applications of strongly correlated oxides.

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Oxygen Vacancies Allow Tuning the Work Function of Vanadium Dioxide

Wang

Katase

et al. 2018

Adv Materials Inter

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over a wide range by substitutional doping and external strain, etc. [3] Due to these remarkable features, VO 2 has in addition to its potential use as electrode, [4] applications such as optical switching devices, [5] memory devices, [6] and smart windows. [7] At room temperature (RT), undoped VO 2 is in the insulating state and for most VO 2 thin films the work function is moderately high (up to 5.55 eV). [8] Thus, VO 2 has not been considered as a suitable hole injecting electrode as for related hole injecting transition metal oxides, the work function is usually >6.0 eV. [9] However, recently we could show that the work function of VO 2 can reach up to 6.70 eV and, moreover, even in the insulating state at RT, the conductivity is sufficient to allow for adequate charge transport. [4] VO 2 is yet a complex material and although the MIT was discovered already in 1959, [2a] it is still under debate whether it is induced by Mott-Hubbard correlation or due to a structural Peierls-type transition, or both. [10] Consequently, also the underlying reasons that enable achieving high work function are largely unexplored. It can be speculated that for VO 2 , as for other transition metal oxides, the work function is related to the stoichiometry. [11] Vanadium, with an electronic configuration of [Ar]3d 3 4s 2 , can form multivalent oxides with different valence states, like VO, V 2 O 5 , V 2 O 3 , V 6 O 13 , and VO 2 . [12] It is thus essential to have a comprehensive understanding of the electronic properties of an actual surface in order to use it in practical devices. [13] The evolution of electron valence bands, core levels, and work function of vanadium dioxide (VO 2 ) thin films upon argon ion sputtering and annealing, as commonly done to obtain atomically clean surfaces, with and without low-pressure oxygen atmosphere during annealing is investigated by ultraviolet and X-ray photoemission spectroscopy. Both sputtering and annealing in vacuum introduce lower oxidation state V species, leading to an increased intensity of V 3d derived bands close to the Fermi level. Such oxygen deficient surfaces exhibit low work function values as low as 4.40 eV. Annealing the sample under low-pressure oxygen atmosphere (few times 10 −4 mbar partial O 2 pressure) results in stoichiometric VO 2 surfaces with a high work function of up to 6.70 eV. Moreover, the work function of the VO 2 can be continuously tuned between the high and low limits by adjusting the atomic ratio of oxygen and vanadium at the surface. Appropriately adjusted VO 2 can thus be employed as moderate electron as well as superior hole injecting electrode material in electronic and optoelectronic devices. Figure 6. Correlation of work function and atomic ratio (O to V). www.advancedsciencenews.com

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Photoemission study of the metal-insulator transition inVO2/TiO2(001):

Cited by 107 publications

References 36 publications

VO ₂ : A two-fluid incoherent metal?

VO ₂ : A two-fluid incoherent metal?

Versatile Tunability of the Metal Insulator Transition in (TiO₂)_m/(VO₂)_m Superlattices

Oxygen Vacancies Allow Tuning the Work Function of Vanadium Dioxide

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Photoemission study of the metal-insulator transition inVO2/TiO2(001):

Cited by 107 publications

References 36 publications

VO 2 : A two-fluid incoherent metal?

VO 2 : A two-fluid incoherent metal?

Versatile Tunability of the Metal Insulator Transition in (TiO2)m/(VO2)m Superlattices

Oxygen Vacancies Allow Tuning the Work Function of Vanadium Dioxide

Contact Info

Product

Resources

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VO ₂ : A two-fluid incoherent metal?

VO ₂ : A two-fluid incoherent metal?

Versatile Tunability of the Metal Insulator Transition in (TiO₂)_m/(VO₂)_m Superlattices