Large phonon band gap in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi mathvariant="normal">Sr</mml:mi><mml:mi mathvariant="normal">Ti</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math>and the vibrational signatures of ferroelectricity in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>A</mml:mi><mml:mi mathvariant="normal">Ti</mml:mi><mml:msub><mml:mi mathvarian

Recent experimental data on the optical conductivity of niobium doped SrTiO3 are interpreted in terms of a gas of large polarons with effective coupling constant α ef f ≈ 2. The theoretical approach takes into account many-body effects, the electron-phonon interaction with multiple LOphonon branches, and the degeneracy and the anisotropy of the Ti t2g conduction band. Based on the Fröhlich interaction, the many-body large-polaron theory provides an interpretation for the essential characteristics, except -interestingly -for the unexpectedly large intensity of a peak at ∼ 130 meV, of the observed optical conductivity spectra of SrTi1−xNbxO3 without any adjustment of material parameters.

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“…[41] and references therein). The effect of the phonon dispersion is a broadening of features of the polaron optical conductivity band.…”

Section: Optical Conductivity Of a Gas Of Large Polaronsmentioning

confidence: 99%

Many-body large polaron optical conductivity inSrTi1−xNbxO3

et al. 2010

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“…ω [9]). This case thereby presents the example of the phonon-mediated superconductivity in the extreme anti-adiabatic limit 0 In the opposite limit 0 / F E ω >> electrons of the pair sense instantaneously and at the same time both the direct Coulomb repulsion and the potential created by the local lattice distortion.…”

Section: Introductionmentioning

confidence: 99%

Superconducting transition temperature: Interacting Fermi gas and phonon mechanisms in the nonadiabatic regime

Gor’kov

2016

Phys. Rev. B

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We analyze the mathematical structure of equations for temperature of the superconductivity transition in a gas of interacting Fermi particles or at the phonon-mediated pairing in a metal in case of non-adiabatic conditions, when the characteristic phonon frequency 0 ω is comparable or larger than the Fermi energy . The integral equations for are derived in the logarithmical approximation. The equations contain no divergent terms in the anti-adiabatic limit.

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“…Furthermore, as pointed out by Choudhury et al, the zone-center phonons in unstrained perovskites exhibit interesting frequency gaps. 46 These phonon gaps may have innovative applications in sound and heat revolutions.…”

Section: A Mode Sequence In Strained Batio3mentioning

confidence: 99%

Mode sequence, frequency change of nonsoft phonons, and LO-TO splitting in strained tetragonalBaTiO3

Raeliarijaona

2015

Phys. Rev. B

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Ultraviolet Raman spectroscopy revealed the existence of an unusual large frequency shift occurring to a non-soft mode of E(TO4) when BaTiO3 is strained to a SrTiO3 substrate [D. Tenne et al., Science 313, 1614]. It raised two interesting questions: (i) whether there are other non-soft modes that possess similar or even larger strain-induced frequency shifts; (ii) how the mode sequence is altered by these shifts in frequency. Note that mode sequence is also pivotal in correctly indexing and assigning the spectroscopy peaks observed in all Raman experiments. By mapping out the evolutions of individual phonon modes as a function of strain using first-principles density functional perturbation calculations, we determine the mode sequence and strain-induced phonon frequency shifts in prototypical BaTiO3. Our study reveals that the mode sequence is drastically different when BaTiO3 is strained to SrTiO3 as compared to that in the unstrained structure, caused by multiple mode crossings. Furthermore, we predict that three other non-soft modes-A1(TO2), E(LO4), and A1(TO3)-display even larger strain-induced frequency shifts than E(TO4). The strain responses of individual modes are found to be highly mode specific, and a mechanism that regulates the magnitude of the frequency shift is provided. As another key outcome of this study, we tackle a long-standing problem of LO-TO splitting in ferroelectrics. A rigorous definition for the LO-TO splitting is formulated, which allows this critical quantity to be calculated quantitatively. The definition immediately reveals a new finding, that is, a large LO-TO splitting not only exists for E(LO4), which is previously known and originates from a soft mode, it also occurs to a non-soft A1(LO3) mode. The LO-TO splitting is shown to decrease drastically with compressive strain, and this decrease cannot be explained by the Born effective charges and high-frequency dielectric constants.

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Large phonon band gap inSrTiO3and the vibrational signatures of ferroelectricity inATi

Cited by 96 publications

References 68 publications

Many-body large polaron optical conductivity inSrTi1−xNbxO3

Many-body large polaron optical conductivity inSrTi1−xNbxO3

Superconducting transition temperature: Interacting Fermi gas and phonon mechanisms in the nonadiabatic regime

Mode sequence, frequency change of nonsoft phonons, and LO-TO splitting in strained tetragonalBaTiO3

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