Infrared reflectivity studies of ceramic YBa2Cu4O8

Buckley, R. G.; Staines, M.P.; Haines, E. M.; Ziaei, M. E.; Clayman, B. P.

doi:10.1016/0921-4534(94)91843-0

Cited by 6 publications

(6 citation statements)

References 6 publications

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“…It is the purpose of this paper to report new results which indicate that Bi superconductors do indeed show large phonon softening in the superconducting phase with an onset at temperatures slightly above T c . Similar ob-servations in other superconducting materials were reported in [9][10][11][12].…”

Section: Introductionsupporting

confidence: 88%

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Phonon softening and MIR absorption in superconducting

Zhigadlo

Zhang

Salje

1997

Supercond. Sci. Technol.

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The temperature evolution of the far-infrared (FIR) and mid-infrared (MIR) absorption spectra of Bi 1.7 Pb 0.3 Sr 2 Ca 2 Cu 3 O 10+x (2223 phase) superconductors show a large softening of phonon frequencies in the superconducting phase ( ω/ω ≈ 7 × 10 −3 ). The onset of the softening is at 130 K which is well above the superconducting transition temperature at 106 K. A change of the MIR absorption near T c is reported and compared with earlier observations in YBa 2 Cu 3 O 7 .

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Section: Introductionsupporting

confidence: 88%

“…The spectral line shift is comparable in size with those of YBCO-based superconductors. For example, in YBCO samples [9][10][11][12] (doped 123 compounds, oxygen-deficient ones and 124-YBCO), the overall softening is of 4-8 cm −1 while in LSCO samples [14] the softening of 0.2-0.3 cm −1 is much weaker.…”

Section: Resultsmentioning

confidence: 99%

Phonon softening and MIR absorption in superconducting

Zhigadlo

Zhang

Salje

1997

Supercond. Sci. Technol.

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“…Neutron pair distribution functions [518] find local distortions of both planar, apical, and chain related O's, which have the same temperature dependence as the pseudogap. When the hole doping in Y-124 is varied by cation substitution, the doping dependence of the pseudogap is found to be similar to that found in YBCO [519]. Whereas no elastic or heat capacity anomalies are found in pure YBa 2 Cu 4 O 8 near the pseudogap, in Ca substituted samples there are clear anomalies in both properties at 150K, strongly suggestive of a second-order phase transition [520,521].…”

Section: Experimental Observationsmentioning

confidence: 72%

A survey of the Van Hove scenario for high-tc superconductivity with special emphasis on pseudogaps and striped phases

Markiewicz

1997

Journal of Physics and Chemistry of Solids

371

280

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The Van Hove singularity (VHS) provides a paradigm for the study of the role of peaks in the density of states (dos) on electronic properties. More importantly, it appears to play a major role in the physics of the high-Tc superconductors, particularly since recent photoemission studies have found that the VHS is close to the Fermi level in most of the high-Tc cuprates near the composition of optimum Tc. This paper offers a comprehensive survey of the VHS model, describing both theoretical properties and experimental evidence for the picture. Special topics discussed include a survey of the Fermi surfaces of the cuprates and related compounds, and an analysis of the reliability of the slave boson approach to correlation effects. While many properties of the cuprates can be qualitatively understood by a simple rigid-band-filling model, this is inadequate for more quantitative results, since correlation effects tend to pin the Fermi level near the VHS over an extended doping range, and can lead to a nanoscale phase separation. Furthermore, the peaks in the dos lead to competition from other instabilities, both magnetic and structural (related to charge density waves). A novel form of dynamic structural instability, involving dynamic VHS-Jahn-Teller effects has been predicted. Scattered through the literature, there is considerable experimental evidence for both nanoscale phase separation of holes, and for local, possibly dynamic, structural disorder. This review attempts to gather these results into a comprehensive database, to sort the results, and to see how they fit into the Van Hove scenario. Recent experiments on underdoped cuprates are found to provide a strong confirmation that the pseudogap is driven by a splitting of the VHS degeneracy.

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“…Thus the antiferromagnetic correlation becomes stronger as YBCO is reduced. The phonon anomalies were optically investigated by systematically changing the doping level, and a certain phonon softening was noted above Tc for underdoped materials [1102][1103][1104][1105]. In a strong-coupling superconductor, there often occurs a phonon softening above Tc.…”

Section: Yba2cu307-rementioning

confidence: 99%