Frequency dependence of the electrical conductivity of small polarons for high and low temperatures

Reik, H.G.; Heese, D.

doi:10.1016/0022-3697(67)90089-3

Cited by 177 publications

(67 citation statements)

References 39 publications

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“…Virtually no temperature dependence of this feature is observed down to 40 K. This behaviour allows us to rule out the presence of small polarons, which would require a strong temperature dependence of the mid-IR absorption. 26 Large polaron absorption spectra, on the other hand, are expected to be temperature independent and asymmetric, 27 in agreement with our data. The peak position near 0.3 eV is also consistent with large polarons, as it is below the 0.7 eV cut off predicted by Fröhlich coupling for transition metal oxides 23 .…”

Section: 25supporting

confidence: 88%

Optical probe of strong correlations in LaNiO3 thin films

Stewart¹,

Liu²,

Smith³

et al. 2011

Journal of Applied Physics

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The optical properties of LaNiO3 thin films are investigated over a wide energy and temperature range. Thin films of varying thickness were epitaxially grown by pulsed laser deposition on LaAlO3 and SrTiO3 substrates. The optical conductivity data of the films reveal a number of interband transitions above 1 eV which are in good agreement with band structure calculations. No well defined Drude peak is observed however, in stark contrast with LDA theory predicting a finite density of states at the Fermi energy. This experimental finding of a vanishing Drude spectral weight, compared to a finite electron kinetic energy obtained from band structure calculations, highlights the importance of strong electronic correlations in LaNiO3.

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Section: 25supporting

confidence: 88%

Optical probe of strong correlations in LaNiO3 thin films

Stewart¹,

Liu²,

Smith³

et al. 2011

Journal of Applied Physics

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“…11,52,53 In the present study only amorphous tungsten oxide films are investigated and the below-band-gap spectral region is considered. According to the frequency-dependent electrical conductivity theory of Reik and Heese 54 and Schirmer et al, 55 the polaron contribution to the DF is described by a single Gaussian line shape or alternatively by a harmonic Lorentzian-broadened oscillator. 2,32,56,57 It has already been observed that a single Gaussian or Lorentzian line shape is not fully sufficient to describe the experimentally observed absorption behavior.…”

Section: Polaron Contributionmentioning

confidence: 99%

Polaron and phonon properties in proton intercalated amorphous tungsten oxide thin films

et al. 2008

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We report on the evolution of the polaron and phonon mode properties in amorphous tungsten oxide thin films measured by spectroscopic ellipsometry in the infrared to ultraviolet spectral regions as a function of the intercalated proton density. A parametric physical model dielectric function is presented, which excellently describes the ellipsometry data over a large intercalated charge-density range. Upon increased amounts of intercalated charge we observe a strong increase in the polaron absorption in the visible spectral range, a decrease in the infrared W-O bond polarity, and an increase in the W = O bond polarity. Our findings support the oxygen-extraction model as the polaron formation mechanism in tungsten oxide in agreement with previous theoretical works based on first-principles pseudopotential calculations. We discuss and suggest polaron formation by oxygen-related defect generation as origin for the coloration mechanism in tungsten oxide. We further discuss possible evidence for very large effective mass of the polarons within the insulator-to-metal transition regime.

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“…Starting from |Φ 0 i, one generates an orthonormal set of states f|Φ n ig by successively operating with H on |Φ n i, n = 0, ⋅ ⋅ ⋅ , M, and orthonormalizing to all the previous vectors, such that the Hamiltonian is represented by a real symmetric well as in the strong coupling case [24] using perturbative methods. However, in none of the approaches used were the polaron-polaron interactions taken into account, i. e., the results are only trustworthy (especially in the strong coupling limit) in the single polaron limit.…”

Section: Numerical Treatment Of the T-j Holstein Hamiltonianmentioning

confidence: 99%

Conductivity ofCuO3chains: Disorder versus electron-phonon coupling

Fehrenbacher

1994

Phys. Rev. B

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The optical conductivity of the CuO 3 -chains, a subsystem of the 1-2-3 materials, is dominated by a broad peak in the mid-infrared (ω ≈ 0.2eV), and a slowly falling high-frequency tail. The 1D t-J-model is proposed as the relevant low-energy Hamiltonian describing the intrinsic electronic structure of the CuO 3 -chains. However, due to charge-spin decoupling, this model alone cannot reproduce the observed σ (ω). We consider two additional scattering mechanisms: (i) Disregarding the not so crucial spin degrees of freedom, the inclusion of strong potential disorder yields excellent agreement with experiment, but suffers from the unreasonable value of the disorder strength necessary for the fit. (ii) Moderately strong polaronic electron-phonon coupling to the mode involving Cu(1)-O(4) stretching, can be modeled within a 1D Holstein Hamiltonian of spinless fermions. Using a variational approximation for the phonon Hilbert space, we diagonalize the Hamiltonian exactly on finite lattices. As a result of the experimental hole density ≈ 1/2, the chains can exhibit strong charge-density-wave (CDW) correlations, driven by phonon-mediated polaron-polaron interactions. In the vicinity of half filling, charge motion is identified as arising from moving domain walls, i. e., defects in the CDW. Incorporating the effect of vacancy disorder by choosing open boundary conditions, good agreement with the experimental spectra is found.In particular, a high-frequency tail arises as a consequence of the polaron-polaron interactions.

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Frequency dependence of the electrical conductivity of small polarons for high and low temperatures

Cited by 177 publications

References 39 publications

Optical probe of strong correlations in LaNiO3 thin films

Optical probe of strong correlations in LaNiO3 thin films

Polaron and phonon properties in proton intercalated amorphous tungsten oxide thin films

Conductivity ofCuO3chains: Disorder versus electron-phonon coupling

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