New Insights into the Diverse Electronic Phases of a Novel Vanadium Dioxide Polymorph: A Terahertz Spectroscopy Study

Lourembam, James; Srivastava, Amar; La-o-vorakiat, Chan; Rotella, H.; Venkatesan, T.; Chia, Elbert E. M.

doi:10.1038/srep09182

Cited by 39 publications

(47 citation statements)

References 57 publications

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“…According to Hall-effect measurements, the carrier density in VO 2 increases by~10 4 across the SMT [50] while according to optical measurements, the effective mass of the carriers is m *~2 m e above the transition temperature [51]. For VO 2 at 100 C and considering m * ¼ 2m e , the carrier density calculated from the plasma frequency is n z 1.04 Â 10 21 cm À3 while calculation of the mobility of the carriers from t DS ¼ m * m ð1þcÞe gives m z 13.6 cm 2 /V s, which are both similar to values reported from THz-TDS spectroscopy measurements [29,41].…”

Section: Conductivity Models and The Drude-smith Formalismsupporting

confidence: 77%

“…Various attempts of analyzing and modelling the THz conductivity spectra of VO 2 thin films were reported using the effective medium theory (EMT) [28,39,40], which is suggested by the presence of separated metallic and semiconducting phases in the films. The lack of consistency of the results reported from such analysis arises from the difficulty of EMT to accurately model the behavior of the far-infrared conductivity in the vicinity of the SMT by simply using the optical constants of semiconducting and metallic phases [41]. Indeed, the properties of the newly-formed metallic puddles at the onset of the transition and those of the high temperature metallic phase are observed to differ.…”

Section: Conductivity Models and The Drude-smith Formalismmentioning

confidence: 99%

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Natural metamaterial behavior across the phase transition for WxV1−xO2 films revealed by terahertz spectroscopy

et al. 2017

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Metamaterials, which are made of repeated patterns of appropriately arranged small discrete structures, display unusual electromagnetic properties that overwhelm those of conventional materials. The modification of their properties is generally achieved by arranging the structures mechanically or electrically and requires rather complex designs. We report on the study of the complex conductivity of epitaxially-grown tungsten-doped vanadium dioxide (W x V 1Àx O 2) thin films through the semiconductorto-metal phase transition (SMT) using terahertz time-domain spectroscopy. The modelling of the terahertz conductivity across W x V 1Àx O 2 SMT provides clear insights about the gradual nucleation of VO 2 metallic domains among the semiconducting host and evidences the presence of strong carrier confinement and enhanced absorption close to the transition temperature, leading to a strong capacitive response of the electrons. The evolution of the SMT is also strongly affected by W doping, which reduces the scattering time in the metallic state, lowers the transition onset temperature and extends the temperature range over which the transition occurs. The W x V 1Àx O 2 films thus forms an effective medium in the vicinity of the SMT and display the signature of a disordered metamaterial, which has significantly enhanced functionality thanks to its readily thermally-tunable properties over a wide range of temperatures close to room temperature.

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Section: Conductivity Models and The Drude-smith Formalismsupporting

confidence: 77%

Section: Conductivity Models and The Drude-smith Formalismmentioning

confidence: 99%

Natural metamaterial behavior across the phase transition for WxV1−xO2 films revealed by terahertz spectroscopy

et al. 2017

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“…[155] Figure 8 shows the THz real and imaginary conductivity as a function of temperature for VO 2 (B) and VO 2 (M1) across the M-I transition. [155] Figure 8 shows the THz real and imaginary conductivity as a function of temperature for VO 2 (B) and VO 2 (M1) across the M-I transition.…”

Section: Study Of M-i Transition In Vanadates Using Thz-tdsmentioning

confidence: 99%

“…In a report by Kim et al, [157] it was concluded from THz transmission measurements that the structural and electronic phase transitions occur independently where T M-I was observed at a temperature lower than T SPT. [155] Copyright 2015, Springer Nature. Optical Mater.…”

Section: Study Of M-i Transition In Vanadates Using Thz-tdsmentioning

confidence: 99%

Terahertz Electrodynamics in Transition Metal Oxides

Prajapati

Dagar

et al. 2019

Advanced Optical Materials

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The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adom.201900958. 2−y 2 , d z 2 ) levels. [35] The splitting of the d-orbital was successfully explained by the crystal field theory. The ground state properties of these materials are mainly governed by the two interactions; i) the electron correlations (U) and, ii) SOC (λ) in the crystal field split narrow bands. [36] Among d electron systems, electrons in 3d TMOs experiences large electron correlations due to localized nature of 3d orbitals. The idea of electron-electron interaction was given by Sir N. F. Mott in 1949. It originated from the fact that the NiO was expected to be a metal according to the band theory, while the experiments showed insulating behavior. [37][38][39][40][41] This disagreement of experiments with the theory was explained by Hubbard who attributed the insulating state to the splitting

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“…21,26,27 Terahertz spectroscopy has also been used to study metallic domain evolution through the conductivity signatures of carrier localization. 22,27,36,38 This has yielded insights into the average dynamics of nanodomains, but the local influence of defects, crystallinity, and strain have remained out of reach because far-field spectroscopy is an inherently macroscopic technique. Meanwhile, scattering-type near-field scanning optical microscopy (s-NSOM) in the terahertz and mid-infrared has proven uniquely suited to investigating the local behavior of the steady-state transition.…”

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confidence: 99%

Ultrafast Mid-Infrared Nanoscopy of Strained Vanadium Dioxide Nanobeams

et al. 2016

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Long regarded as a model system for studying insulator-to-metal phase transitions, the correlated electron material vanadium dioxide (VO 2 ) is now finding novel uses in device applications. Two of its most appealing aspects are its accessible transition temperature (∼341 K) and its rich phase diagram. Strain can be used to selectively stabilize different VO 2 insulating phases by tuning the competition between electron and lattice degrees of freedom. It can even break the mesoscopic spatial symmetry of the transition, leading to a quasiperiodic ordering of insulating and metallic nanodomains. Nanostructuring of strained VO 2 could potentially yield unique components for future devices. However, the most spectacular property of VO 2  its ultrafast transitionhas not yet been studied on the length scale of its phase heterogeneity. Here, we use ultrafast near-field microscopy in the mid-infrared to study individual, strained VO 2 nanobeams on the 10 nm scale. We reveal a previously unseen correlation between the local steady-state switching susceptibility and the local ultrafast response to below-threshold photoexcitation. These results suggest that it may be possible to tailor the local photoresponse of VO 2 using strain and thereby realize new types of ultrafast nano-optical devices. KEYWORDS: Near-field, femtosecond dynamics, VO 2 , NSOM, phase transition, correlated electrons T he insulator-to-metal phase transition in vanadium dioxide (VO 2 ) has been the subject of extensive investigation since its discovery in 1959 (ref 1). Interest has stemmed in part from its relatively simple, nonmagnetic structure 2 and its accessible transition temperature (T c ∼ 341 K), which makes it relevant for technological applications.3−6 Nevertheless, the enduring appeal of VO 2 can be traced to the complex interplay between electron and lattice degrees of freedom that produce its intricate free-energy landscape. 7−12 This fine balance between competing interactions can be tuned by strain, leading to a rich phase diagram.13,14 Below T c , unstrained VO 2 is an insulator characterized by both strong electron−electron correlations and lattice distortion, where the vanadium ions form chains of dimerized pairs (monoclinic structure, M1). These dimers are dissociated in the rutile (R), metallic phase (T > T c ) in a process reminiscent of a Peierls transition. However, cluster dynamical mean-field theory calculations have shown that both lattice distortion and strong on-site electron− electron Coulomb repulsion are necessary to accurately model the band gap.9 Moreover, tensile strain applied to the insulating state can produce new, stable lattice structures that are intermediates between M1 and R and, surprisingly, these states are also insulators. High tensile strain along the rutile c R axis (>2%, along the direction of the dimerized chains in the insulating state) induces the monoclinic insulating phase M2 in which only every second row of vanadium ions is dimerized. 15,16 Meanwhile, moderate tensile strain results in...

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New Insights into the Diverse Electronic Phases of a Novel Vanadium Dioxide Polymorph: A Terahertz Spectroscopy Study

Cited by 39 publications

References 57 publications

Natural metamaterial behavior across the phase transition for WxV1−xO2 films revealed by terahertz spectroscopy

Natural metamaterial behavior across the phase transition for WxV1−xO2 films revealed by terahertz spectroscopy

Terahertz Electrodynamics in Transition Metal Oxides

Ultrafast Mid-Infrared Nanoscopy of Strained Vanadium Dioxide Nanobeams

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