Phonons in Nd2−xCexCuO4

Heyen, E. T.; Kliche, G.; Kress, W.; König, W.; Cardona, M.; Rampf, E.; Prade, J.; Schröder, U.; Kulkarni, Anil D.; Wette, F. W. de; Piñol, S.; Paul, D. McK.; Morán, E.; Alario-Franco, M.A.

doi:10.1016/0038-1098(90)90996-o

Cited by 79 publications

(40 citation statements)

References 13 publications

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“…In addition to the CuO1 bond-stretching mode (E u ) at the highest energy, there is the CuO1 bondbending mode (E u ) at about 10THz, the B g -mode at 10.3 THz and the O2-mode (E u ) at 9.4 THz. The B gmode corresponds to a motion of O2 parallel to the caxis; its frequency is observed by Raman-scattering at 10.0-10.3 THz [39,40,41]. E u -modes are Infra-Red active; however, the reported measurements are not conclusive, possibly due to insufficient sample quality [41,42].…”

Section: Iii2 Phonon Dispersion In [100] Directionmentioning

confidence: 96%

Dispersion of the high-energy phonon modes inNd1.85Ce0.15CuO4

et al. 2005

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The dispersion of the high-energy phonon modes in the electron doped high-temperature superconductor Nd1.85Ce0.15CuO4 has been studied by inelastic neutron scattering. The frequencies of phonon modes with Cu-O bond-stretching character drop abruptly when going from the Brillouin zone center along the [100]-direction; this dispersion is qualitatively similar to observations in the hole-doped cuprates. We also find a softening of the bond-stretching modes along the [110]-direction but which is weaker and exhibits a sinusoidal dispersion. The phonon anomalies are discussed in comparison to hole-doped cuprate superconductors and other metallic perovskites.

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Section: Iii2 Phonon Dispersion In [100] Directionmentioning

confidence: 96%

Dispersion of the high-energy phonon modes inNd1.85Ce0.15CuO4

et al. 2005

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“…21 Kramers doublets have also been reported in the Raman spectra at low temperature, 48 which have been attributed to the removal of degeneracy by the Nd-Cu exchange interaction. 49 While this is a reasonable explanation for the strong feature at low frequency, it is less satisfactory for the fine structure observed at high frequency.…”

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confidence: 92%

“…19 In fact, due to the sigTypeset by REVT E X nificant exchange interactions between the Pr ions which are mediated through the copper-oxygen layers, there is a Pr contribution to the susceptibility 12 below ≈ 200 K. The optical properties of Nd 2 CuO 4 have been investigated in ceramics and single crystals. 20,21,22,23,24,25,26,27 Single crystals of Pr 2 CuO 4 have been studied at either room temperature 28,29,30,31 or at low temperature 11,32 (≈ 10 K), but there has been no detailed investigation of the temperature dependence of the optical properties of this material. Furthermore, there is some disagreement in the literature with respect to the vibrational parameters of the E u modes.…”

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confidence: 99%

“…This view is consistent with the observation that this new feature is not present in Pr 1.85 Ce 0.15 CuO 4 , which is in the region of the phase diagram for this class of materials where the AFM order is destroyed. 21 Because the other E u modes do not involve strong Pr-Cu coupling, no exchange-induced splitting would be expected. In fact, of all the other vibrational modes, only the low-frequency A 2u mode has a significant Pr-Cu interaction (Table III), but since this mode is singly degenerate no splitting is expected, nor it is observed.…”

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confidence: 99%

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Infrared optical properties ofPr2CuO4

Homes

Fournier

et al. 2002

Phys. Rev. B

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The ab-plane reflectance of a Pr2CuO4 single crystal has been measured over a wide frequency range at a variety of temperatures, and the optical properties determined from a Kramers-Kronig analysis. Above ≈ 250 K, the low frequency conductivity increases quickly with temperature; ρ dc ≈ 1/σ1(ω → 0) follows the form ρ dc ∝ exp(Ea/kBT ), where Ea ≈ 0.17 eV is much less than the inferred optical gap of ≈ 1.2 eV. Transport measurements show that at low temperature the resistivity deviates from activated behavior and follows the form ρ dc ∝ exp[(T0/T ) 1/4 ], indicating that the dc transport in this material is due to variable-range hopping between localized states in the gap. The four infrared-active Eu modes dominate the infrared optical properties. Below ≈ 200 K, a striking new feature appears near the low-frequency Eu mode, and there is additional new fine structure at high frequency. A normal coordinate analysis has been performed and the detailed nature of the zone-center vibrations determined. Only the low-frequency Eu mode has a significant Pr-Cu interaction. Several possible mechanisms related to the antiferromagnetism in this material are proposed to explain the sudden appearance of this and other new spectral features at low temperature.

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“…Most experiments on c-axis dynamics [9,10] were carried out using ceramic NCCO samples. Alternatively, the method of grazing-incidence reflection is known to be powerful in extracting the c-axis properties of strongly anisotropic superconductors [11].…”

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confidence: 99%

Submillimeter spectroscopy of tilted Nd1.85Ce0.15CuO4−δ films: Observation of a mixed ac-plane excitation

Pimenov

Пронин

Loidl

et al. 2000

Applied Physics Letters

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The anisotropic conductivity of a series of tilted Nd1.85Ce0.15CuO 4−δ thin films was measured by quasioptical spectroscopy in the frequency range 3 cm −1 < ν < 40 cm −1 . Two characteristic features have been observed in the low-temperature transmission spectra. The first one at ν = 12 cm −1 was shown to reflect the c-axis plasma frequency of Nd1.85Ce0.15CuO 4−δ . The second feature represents a new mixed ab-plane/c-axis excitation. The frequency of this resonance may be changed in a controllable way by rotating the polarization of the incident radiation.Among the cuprate superconductors, Nd 2−x Ce x CuO 4 (NCCO) has attracted considerable interest because it can be considered as electron-doped compound [1], which reveals the (T ′ ) tetragonal structure and is extremely two-dimensional [1,2]. Earlier in-plane microwave experiments on NCCO [3][4][5] appeared to be consistent with the conventional s-wave BCS predictions. However, recent data including flux quantization [6] and penetration depth at microwaves [7] and at radiowaves [8] provided strong experimental evidence of d-wave symmetry of the pairing state.In contrast to a number of ab-plane experiments, there exists only few information concerning the c-axis properties of NCCO due to small dimensions of the samples along the c-axis. Most experiments on c-axis dynamics [9,10] were carried out using ceramic NCCO samples. Alternatively, the method of grazing-incidence reflection is known to be powerful in extracting the c-axis properties of strongly anisotropic superconductors [11]. The experiments using instead of the grazing reflection a tilted sample [12] and the normal-incidence geometry may be considered as modification of this method.In this letter we present the results of submillimeterwave (3 cm −1 < ν < 40 cm −1 ) experiments on tilted Nd 1.85 Ce 0.15 CuO 4−δ films at low temperatures. The spectra reveal two new features below the superconducting transition, which could be identified as: i) plasma resonance along the c-axis and ii) mixed ab-plane/c-axis excitation. Using the measurements at different polarizations of the incident radiation it was possible to separate the effective conductivity at a tilted angle into components within the ab-plane and along the c-axis.The experiments were carried out on different Nd 1.85 Ce 0.15 CuO 4−δ films yielding similar results. For simplicity, the results from only one film are presented. The films were prepared using a two-beam-laser deposition on yttrium stabilized ZrO 2 substrates [13]. X-ray analysis revealed the c-axis orientation of the films. The substrate of the presented film was tilted from (001) plane by an angle α = 0.8 o ± 0.4 o . Therefore, the film was also tilted by the same angle from the ideal c-axis orientation. The ac-susceptibility measurements revealed a narrow superconducting transition (∆T [10% − 90%] = 0.9 K) with the onset temperature of 20.1 K. The film thickness, estimated from the deposition time, was d = 170 nm.The transmission experiments in the frequency range 6 cm −1 < ν < 40 cm −...

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Phonons in Nd2−xCexCuO4

Cited by 79 publications

References 13 publications

Dispersion of the high-energy phonon modes inNd1.85Ce0.15CuO4

Dispersion of the high-energy phonon modes inNd1.85Ce0.15CuO4

Infrared optical properties ofPr2CuO4

Submillimeter spectroscopy of tilted Nd1.85Ce0.15CuO4−δ films: Observation of a mixed ac-plane excitation

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