Phonon anomalies and range of superconducting energy gaps from infrared studies of YBa2Cu3O7−δ
L. Genzel, A. Wittlin, M. Bauer, M. Cardona, E. Schönherr, A. Simon
DOI 10.1103/PhysRevB.40.2170 · Physical Review B
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Abstract
The infrared reflectivity of sintered YBa2Cu3O7−δ, prepared under carefully controlled oxidation conditions, has been measured between 20 and 10 000 cm−1 at temperatures between 10 and 300 K. In this paper we analyze in detail the temperature- and frequency-dependent far-infrared part of the spectrum. A Kramers-Kronig analysis allows us to compare the phonon part of the spectra with lattice-dynamical calculations. There is fairly good agreement concerning the assigned eigenfrequencies. The oscillator strengths of the experimentally observed phonons, however, are all stronger than those from a lattice-dynamics model which assumes ionic charges close to the formal ones. This is especially so for the lowest phonon found at 155 cm−1 which shows a strength S=60±5 being about 15 times higher than theoretically expected. A possible origin of this effect is discussed qualitatively in terms of a Cu(1)-O(IV) charge shift during the vibration induced by the polarization field. The electronic background of the spectra has been analyzed by a Mattis-Bardeen type of dielectric response below Tc. The best fit yielded, for low T, a gap distribution in the range from about 160 to 370 cm−1, corresponding to 2Δ(0)/kBTc values between 2.6 and 6.0.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| YBa2Cu3O7-δ Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 89 | Pressure not reported | zero_resistance |
| YBa2Cu3O7-δ Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 89 | Pressure not reported | zero_resistance |
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