Optical properties of Nd2−xCexCuO4 thin films

Hirochi, Kumiko; Hayashi, Shigenori; Adachi, Hideaki; Mitsuyu, Tsuneo; Hirao, Takashi; Setsune, Kentaro; Wasa, Kiyotaka

doi:10.1016/0921-4534(89)90061-0

Cited by 35 publications

(8 citation statements)

References 19 publications

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“…From the electronic energy band structure calculations [29] the average Fermi velocity is derived as 4.9×10 7 cm s −1 and the plasma frequency is about 4 eV. The values of the plasma frequency, hω p = 1.07 eV, and the effective mass, m * = 1.9m e , were obtained from the optical reflectivity spectra of superconducting electron-doped cuprates [30]. From the static and dynamic part of the effective interaction potential, one obtains the screening parameter µ * (=0.2) and the electronphonon coupling strength λ(=1.5), the details of which have been given elsewhere [18].…”

Section: Resultsmentioning

confidence: 99%

Interpretation of temperature-dependent resistivity of electron-doped cuprates

Varshney¹,

Choudhary²,

Singh³

2002

Supercond. Sci. Technol.

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The temperature-dependent normal state resistivity of single-crystal Nd1.85Ce0.15CuO4−δ is theoretically analysed within the framework of the classical electron–phonon model of resistivity, i.e. the Bloch–Gruneisen model. Due to inherent acoustic (low-frequency) phonons (ωac) as well as high-frequency optical phonons (ωop), the contributions to the resistivity have first been estimated. The optical phonons of the oxygen-breathing mode yield a relatively larger contribution to the resistivity compared to the contribution of acoustic phonons. The contribution to resistivity estimated by considering both phonons, i.e. ωac and ωop, along with the zero limited resistivity, when subtracted from single-crystal data, infers a quadratic temperature dependence over most of the temperature range (25 ≤ T ≤ 300 K). The quadratic temperature dependence of ρdiff = [ρexp − {ρ0 + ρe-ph( = ρac + ρop)}] is understood in terms of electron–electron inelastic scattering. The comparison of single-crystal experimental data with the present analysis appears to be favourable.

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Section: Resultsmentioning

confidence: 99%

Interpretation of temperature-dependent resistivity of electron-doped cuprates

Varshney¹,

Choudhary²,

Singh³

2002

Supercond. Sci. Technol.

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“…The absence of an anomaly at T N in the resistivity has been observed in many different experiments on LCO and NCO samples. [12][13][14][15] In the relaxationtime approximation, the diffusion contribution S d in S is related to the density of states, the velocity and the relaxation time of conduction electrons, and so is the resistivity ρ in a similar way. [5] Therefore, when S d shows an anomaly at T N , ρ is also expected to show a similar anomaly at the same temperature, as appeared in transition metals [5].…”

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confidence: 99%

Thermopower of high-Tccuprates

Choi

Kim

1999

Phys. Rev. B

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We have studied the thermopower of La2CuO4+z and Nd2CuO4−y which undergo an antiferromagnetic transition near room temperature and Bi2Sr2−xLaxCuO6+z for which a broad spectrum of doping is possible. The thermopower of La2CuO4+z and Nd2CuO4−y is seen to exhibit an anomaly at the Neel temperature, whereas the resistivity is not. The extrapolated zero-temperature intercept of the thermopower, which is known to be positive for hole-doped cuprate superconductors, is found to become negative for Bi2Sr2−xLaxCuO6+z above some critical doping-level. The data strongly suggest that the thermopower of high-Tc cuprates contains a large amount of extra contribution in addition to the usual diffusion thermopower. We discuss origins of the extra contribution in the thermopower.

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“…Presently, EELS of layered materials is of particular interest because the high-T c cuprates have a layered structure. EELS [12] and optical reflectivity [13] have been used to reveal the electronic structure of Nd-Ce-CuO superconductors. These studies reveal a metallic plasma reflection due to free carriers; a plasma frequency of about 1 eV was obtained from the Drude model.…”

Section: Introductionmentioning

confidence: 99%

“…Both plasmons and optical phonons screen the gas of electron carriers which lie in the layered sequence of copper oxide planes and their Coulomb repulsion [14]. The evidence relating to the coupled phonon-electron excitations from Raman [7], infrared [8] and electron-tunnelling [9] spectroscopies associated with the oxygen in Nd-Ce-CuO, together with EELS [12] and reflectance [13] studies of Nd 1.85 Ce 0.15 CuO 4 , have provided the motivation for the present work.…”

Section: Introductionmentioning

confidence: 99%

Transition temperature and oxygen isotope effect of Nd doped cuprates: a three square well model

Varshney

Patel

Singh

2001

Supercond. Sci. Technol.

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Using a three square well model, we investigate the possibility that in low energy plasmons there could be an additional boson responsible for the attractive force binding the Cooper pairs that lead to superconductivity in layered electron-doped cuprates. The three square well model is, in principle, characterized by three coupling strengths, the electron-phonon (λ ph ), the electron-plasmon (λ pl ) and Coulomb screening parameter (µ * ), that estimate the transition temperature (T c ) and oxygen isotope effect coefficient (α). Starting with the three square well model within the framework of the Eliashberg theory, the energy gap kernels allow us to visualize the relative interplay of the Coulomb, electron-phonon and electron-plasmon interactions and we correlate the T c with these three coupling strengths. For a set of parameters (λ ph ≈ 1.0, λ pl ≈ 0.7 and µ * ≈ 0.18), a T c of 28 K is estimated for optimally doped Nd 1.85 Ce 0.15 CuO 4 . The present approach also explains the reported sizeable oxygen isotope effect in electron-doped cuprates. We suggest that the extended attractive force in the proposed three square well scheme consistently explains the superconductivity in electron-doped cuprates.

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Optical properties of Nd2−xCexCuO4 thin films

Cited by 35 publications

References 19 publications

Interpretation of temperature-dependent resistivity of electron-doped cuprates

Interpretation of temperature-dependent resistivity of electron-doped cuprates

Thermopower of high-Tccuprates

Transition temperature and oxygen isotope effect of Nd doped cuprates: a three square well model

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