Anomalous High Pressure Dependence of the Jahn-Teller Phonon in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi>La</mml:mi></mml:mrow><mml:mrow><mml:mn>0.75</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>Ca</mml:mi></mml:mrow><mml:mrow><mml:mn>0.25</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi>MnO</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mm

Congeduti, A.; Postorino, P.; Caramagno, E.; Nardone, M.; Kumar, Ashwani; Sarma, D. D.

doi:10.1103/physrevlett.86.1251

Cited by 96 publications

(101 citation statements)

References 24 publications

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“…Since the Raman spectrum of VO 2 in the R phase is characterized by only 4 broad peaks [29,30] we can safely conclude at a glance that a transition to a R phase is not achieved by applying pressure up to 19 GPa. The good quality of the data allows to apply a standard fitting procedure [20] to analyse the pressure dependence of the phonon spectrum. The analysis shows an almost linear increase of the frequencies of every phonon peak eccept for ω V 1 and ω V 2 at 192 cm −1 and 224 cm −1 at P∼0, respectively, whose pressure dependence is shown in the inset of Fig.…”

Section: Pacs Numbersmentioning

confidence: 99%

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Evidence of a Pressure-Induced Metallization Process in MonoclinicVO2

Arcangeletti¹,

Baldassarre²,

Castro³

et al. 2007

Phys. Rev. Lett.

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191

171

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Raman and combined trasmission and reflectivity mid infrared measurements have been carried out on monoclinic VO2 at room temperature over the 0-19 GPa and 0-14 GPa pressure ranges, respectively. The pressure dependence obtained for both lattice dynamics and optical gap shows a remarkable stability of the system up to P*∼10 GPa. Evidence of subtle modifications of V ion arrangements within the monoclinic lattice together with the onset of a metallization process via band gap filling are observed for P>P*. Differently from ambient pressure, where the VO2 metal phase is found only in conjunction with the rutile structure above 340 K, a new room temperature metallic phase coupled to a monoclinic structure appears accessible in the high pressure regime, thus opening to new important queries on the physics of VO2. PACS numbers:Since the first observation of the metal to insulator transition (MIT) in several vanadium oxides, these materials attracted considerable interest because of the huge and abrupt change of the electrical properties at the MIT. As usual in transition metal oxides, electronic correlation strongly affects the conduction regime of vanadium oxides, although, in some compounds, lattice degrees of freedom seem to play an important role. This is the case of VO 2 , which undergoes a first order transition from a high temperature metallic rutile (R) phase to a low temperature insulating monoclinic (M1) one. At the MIT temperature, T c =340 K, the opening of an optical gap in the mid-infrared (MIR) conductivity and a jump of several order of magnitude in the resistivity are observed [1]. The interest on this compound is thus mainly focused on understanding the role and the relative importance of the electron-electron and the electron-lattice interaction in driving the MIT. Despite the great experimental and theoretical efforts [2], the understanding of this transition is still far from being complete [3,4,5,6,7]. In the R phase the V atoms, each surrounded by an oxygen octahedron, are equally spaced along linear chains in the c-axis direction and form a body-centered tetragonal lattice. On entering the M1 insulating phase the dimerization of the vanadium atoms and the tilting of the pairs with respect to the c axis lead to a doubling of the unit cell, with space group changing from C 5 2h (R) to D 14 4h (M1) [8,9]. As first proposed by Goodenough [10], the V-V pairing and the off-axis zig-zag displacement of the dimers lead to a band splitting with the formation of a Peierls-like gap at the Fermi level. First principle electronic structure calculations based on local density approximation (LDA) showed the band splitting on entering the monoclinic phase, but failed to yield the opening of the band gap [11,12]. In fact, as early pointed out [13], the electron-electron correlation has to be taken into account to obtain the insulating phase. A recent theoretical paper where the electronic Coulomb repulsion U is properly accounted for, shows that calculations carried out joining dynamical mean field theory with...

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Section: Pacs Numbersmentioning

confidence: 99%

“…The gaskets were made of a 250 µm thick steel foil with a sample chamber of 130 µm diameter and 40 to 50 µm height under working conditions. We used NaCl an KBr as pressure transmitting media for Raman and MIR measurements respectively [20,21]. Pressure was measured in situ with the standard ruby fluorescence technique [22].…”

Section: Pacs Numbersmentioning

confidence: 99%

Evidence of a Pressure-Induced Metallization Process in MonoclinicVO2

Arcangeletti¹,

Baldassarre²,

Castro³

et al. 2007

Phys. Rev. Lett.

Self Cite

191

171

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“…But we argue that this is a very clear evidence that the feature up there is second order phonon scattering. In fact, the HFC structure is also present in Sr doped manganites, and all other pseudocubic and double layer manganites [22,23] and we believe that such features are weak second-order Raman scattering effects (density of state), mirroring the bands seen in the region 400-800 cm −1 . The frequencies of the experimental peaks are plotted in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Note that a high frequency oscillator (near 1100 cm −1 ) is necessary to achieve a good fit. It should be pointed out that this High Frequency Contribution (HFC) is also found in Raman experiments on La 0.75 Ca 0.25 MnO 3 [22], and it has been suggested that the HFC should be associated with the photoionization of small polarons. But we argue that this is a very clear evidence that the feature up there is second order phonon scattering.…”

Section: Resultsmentioning

confidence: 99%

The effect of Cu substitution on the A1g mode of La0.7Sr0.3MnO3 manganites

Marzi

Trodahl

Bok

et al. 2003

Solid State Communications

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We report on the first Raman data of Cu substituted La 1−y Sr y Mn 1−x Cu x O 3 (0 ≤ x ≤ 0.10 and 0.17 ≤ y ≤ 0.3, accordingly in order to have the same Mn 4+ /[Mn 4+ +Mn 3+ ] ratio), collected in the frequency range 100-900 cm −1 and at room temperature, with parallel (e i e s ) and crossed (e i ⊥ e s ) polarizations of the incident (e i ) and scattered (e s ) light. Spectra were fitted with a Drude-Lorentz model, and peaks at 190-220 and 430 cm −1 , together with two broad structures centered at near 500 and 670 cm −1 , have been found. We also have observed that the A 1g mode is substantially shifted with increasing Cu substitution. The A 1g phonon shift is a linear function of the tolerance factor t and the rhombohedral angle α r , thus following the structural changes of the MnO 6 octahedra in the system.

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“…Raman spectroscopy is an ideal and relatively straightforward technique to test quantum confinement. Moreover, it can be realized under many extreme and non-extreme conditions, leading to an ideal technique for the investigation of processes in matter at low/high temperatures and/or high pressures (Iwasa et al, 2004;Kim et al, 1996;Wright et al, 1997;Weinstein et al, 1975;Congeduti et al, 2001). Indeed, phonon scattering in crystals of small dimension leads to a redshift and broadening of the first order Raman line.…”

Section: Phonon Quantum Confinement In Nanowiresmentioning

confidence: 99%