Low Temperature Structural Phase Transition and Superconductivity in (La Nd )-Sr-Cu-O

Büchner, B.; Cramm, M.; Braden, M.; Braunisch, W.; Hoffels, O.; Schnelle, Walter; Borowski, R.; Gruetz, A.; B, Heymer; Hohn, C.; Müller, Ralf; Maldonado, O.; Freimuth, A.; Schlabitz, W.; Heger, G.; Khomskii, Daniel I.; Wohlleben, D.

doi:10.1007/978-94-011-2462-1_22

Cited by 8 publications

(7 citation statements)

References 22 publications

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“…The data in Fig. 2 come from experiments on pure Sr doping (summarized by Takahashi, et al [27]), and on Nd substitution studies [28]. Once again, it is found that the transition can be explained equally well by either a purely ionic model, or a mixed ionic, electron-phonon model.…”

Section: B Doping Dependence Of Lto Transitionmentioning

confidence: 81%

Van Hove exciton-cageons and high-Tc superconductivity XB. Polaronic coupling in the doped material

Markiewicz

1995

Physica C: Superconductivity

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A purely ionic interpretation of the tilting mode instabilities in La2−xAxCuO4 (A=Sr,Ba) is shown to be not selfconsistent: the dominant factor influencing the doping dependence of the interlayer mismatch is the large change in the Cu-O bond length. But such a large dependence of bond length on valence leads to a strong electron-phonon coupling, contradicting the assumption that covalent effects were negligible. This coupling is closely related to the vHs-JT effect. This new insight clarifies the role of the tilt-mode instabilities. The main JT coupling is not to these modes, but to the in-plane O-O bond stretching modes which split the vHs degeneracy. However, as these modes soften, they couple to the lower-lying tilt modes, so that the ultimate instability has a finite tilt component.This in turn simplifies the description of the JT instabilities. The tilt modes, while strongly coupled to the electrons, are quadratic in the tilt angle. On the other hand, the bond stretch modes have a large, linear coupling to electrons, with clear polaronic effects. This is connected with the fact that, near a vHs, valence fluctuations are slow and relatively long lived, coupling to local phonon modes. A striking result of this is that there will be a large polaronic band narrowing near the vHs, whether or not the vHs is near the Fermi level. This vHs-localized band narrowing provides a natural explanation for the common occurence of extended vHs's.

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Section: B Doping Dependence Of Lto Transitionmentioning

confidence: 81%

Van Hove exciton-cageons and high-Tc superconductivity XB. Polaronic coupling in the doped material

Markiewicz

1995

Physica C: Superconductivity

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“…At x ≃ 0.15, which has the highest T c when y = 0, there is a sharp, first-order transition when y ≥ 0.18 [884], which is both an LTO-LTT transition and a superconductor-insulator transition. For 0 < y < 0.18, the LTT transition, which would occur at a lower T than the superconducting transition, is arrested at T c , and there appears to be a phase separation, with the Meissner fraction being approximately 1 -(fraction of LTT phase) [425], while there is a small residual fraction of superconducting material at larger y.…”

Section: A Ltt In Lsco:ndmentioning

confidence: 99%

“…A model combining strong VHS-related electron-phonon coupling plus interlayer-strain-induced anharmonicity can explain both the temperature dependence [406] and the doping dependence [150] of the LTO transition. Nd-substitution experiments [425] rule out a pure electron-phonon model since the Nd changes the atomic size without providing any charge transfer; hence, a pure electron-phonon model would predict no change in the transition temperature. On the other hand, photodoping (Section XI.A.5) changes the hole content without modifying the ions, and this too can drive the LTO-HTT transition [426], thereby ruling out a purely ionic model.…”

Section: Tilt-stretch Mode Couplingmentioning

confidence: 99%

“…Starting from the doping of optimum T c , the LTT phase is favored by enhancing the interlayer mismatch, either by decreasing the doping (less Ba,Sr) or by decreasing the average ionic radius at the La site (by substituting Nd, Eu, Gd, Dy, Tb) [425]. Many experiments have used R=Nd, since this can be doped up to y = 0.75 before converting to the T ′ structure (the structure of Nd 2 CuO 4 , the parent compound for the electron-doped superconducting cuprates, with no apical O's).…”

Section: A Ltt In Lsco:ndmentioning

confidence: 99%

“…The magnetic transition may be driven by a critical tilting, due to spin-orbit coupling [366]. There also seems to be a change in the nature of the LTO-LTT transition, at a critical tilt similar to Φ c [425]: for larger Φ values, the transition is sharp and first-order: the orthorhombic splitting of LTO X-ray peaks remains unchanged, while an unsplit LTT peak appears between them, and grows in intensity as the transition procedes. For smaller Φ, the transition is smeared or continuous, with the orthorhombic splitting continuously decreasing as the transition is approached.…”

Section: A Ltt In Lsco:ndmentioning

confidence: 99%

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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

367

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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Microtwin Domains and Phase Transitions in La1.85−x Ndx Sr0.15 CuO4

Kriebel¹,

Gottschalk²,

Büchner³

1992

Phys. Stat. Sol. (a)

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Microstructural phenomena and phase transitions of the Nd‐doped La1.85 Sr0 15 CuO4 system are studied in an electron microscope. In ion‐milled samples, twin domains appear and disappear as expected at the high temperature phase transition. At temperatures below the high temperature transition, these twin domains show a very subtle behaviour. Ground material even in the orthorhombic phase shows no twins at all. In ion‐thinned material a typical reduction of the domain size occurs after an electron illumination time of about one hour. Generally no reversible change of the twin configuration could be observed at the low temperature phase transition.

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Low Temperature Structural Phase Transition and Superconductivity in (La Nd )-Sr-Cu-O

Cited by 8 publications

References 22 publications

Van Hove exciton-cageons and high-Tc superconductivity XB. Polaronic coupling in the doped material

Van Hove exciton-cageons and high-Tc superconductivity XB. Polaronic coupling in the doped material

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

Microtwin Domains and Phase Transitions in La1.85−x Ndx Sr0.15 CuO4

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