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Digitale Medien

Solutions of the Eliashberg equations with abnormally large values of 2Δ(0)/T C (1996)

Barbiellini, B. ; Peter, M. ; Weger, M.

Springer

Journal of superconductivity 9 (1996), S. 59-64

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ISSN: 1572-9605

Schlagwort(e): Superconductivity ; Eliashberg equations ; high-T c cuprates ; organic superconductors

Quelle: Springer Online Journal Archives 1860-2000

Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik

Notizen: Abstract We consider the Eliashberg equations with an electron-phonon matrix elementg(k, k, q) possessing a low-energy cutoffξ 1. In the superconducting state, we assume that this cutoff is bound from below by the superconducting gap 2Δ. We solve for Δ andξ 1 self-consistently, as a function of temperature, and find that the ratio 2Δ(0)/Tc is very large; for parameters that we consider realistic for the cuprates, this ratio is approximately 10. This calculation applies to materials where the mean free path is long (clean limit). We also find that a hysteretic behavior is in principle possible.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00728426

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A new series of mercury-based high-T c superconductors (Hg, W)Sr2(Y1−x Ca x )Cu2 (1996)

Kaibin, Tang ; Yitai, Qian ; Zuyao, Chen ; [weitere]

Springer

Journal of superconductivity 9 (1996), S. 93-95

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ISSN: 1572-9605

Schlagwort(e): Superconductivity ; mercury-based superconductors

Quelle: Springer Online Journal Archives 1860-2000

Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik

Notizen: Abstract A new series of superconducting mercury-based layered cuprates has been synthesized. X-ray diffraction indicates that the compounds with formula Hg0.8W0.2Sr2Y1−x Ca x Cu2O6+δ (0.3≤x≤0.6) exhibit the 1212 structure with space groupP 4/mmm . The investigation of superconductivity determined by electrical resistance measurement shows that the superconducting transition temperature (T c , onset) of Hg0.8W0.2Sr2Y0.4Ca0.6Cu2O6+δ is up to 94 K.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00728432

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Tuning of the Fermi level at the second subband of a superlattice of quantum wires in the CuO2 plane: A possible mechanism to raise the critical temperature (1996)

Saini, N. L. ; Rossetti, T. ; Lanzara, A. ; [weitere]

Springer

Journal of superconductivity 9 (1996), S. 343-348

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ISSN: 1572-9605

Schlagwort(e): Superconductivity ; EXAFS ; superstructure ; quantum wires ; nonhomogeneity

Quelle: Springer Online Journal Archives 1860-2000

Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik

Notizen: Abstract The structure of the stripes in Bi2Sr2CaCu22O8+y superconductor has been refined by polarized CuK-edge extended X-ray absorption fine structure (EXAFS). The distribution of Cu-O (planar) distances range from 1.87 Å to 1.96 Å. The results show that the in-plane CuO2 lattice distortions in the 1D modulation are large enough to form a potential barrier of widthW between the stripes of undistorted CuO2 lattice of widthL=15±0.5 Å. The calculations show that the maximum of the density of states formed by the second subband is tuned to the Fermi level.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00727276

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Effect of gold doping on the superconducting critical temperature and transition width in single-crystal YBa2Cu3Oδ (YBCO) (1996)

Ikuta, H. ; Ginsberg, D. M.

Springer

Journal of superconductivity 9 (1996), S. 259-261

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ISSN: 1572-9605

Schlagwort(e): Superconductivity ; gold-doped YBa2Cu3O−δ ; transition temperature ; transition width

Quelle: Springer Online Journal Archives 1860-2000

Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik

Notizen: Abstract Single-crystal YBa2Cu3O−δ (YBCO) has been made with some of the copper atoms in the copper-oxygen chains replaced by gold. The samples were made by a flux method. The gold concentration was determined by EDX (energy-dispersive X-ray spectroscopy) as a function of the nominal (i.e., flux) composition. Up to about 4.8% of all the copper atoms can be replaced by gold. The effect of the gold doping on the superconducting transition temperature (T c ) and the transition width (ΔT c ) were determined.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00728312

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Metastable states of the 2223 phase in the Bi(Pb)SrCaCuO system (1996)

Velter-Ştefănescu, M. ; Aldica, G. ; Ţoţovână, Alina

Springer

Journal of superconductivity 9 (1996), S. 277-280

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ISSN: 1572-9605

Schlagwort(e): Superconductivity ; Bi2Sr2Ca2Cu3O y ; microwave absorption ; critical temperature

Quelle: Springer Online Journal Archives 1860-2000

Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik

Notizen: Abstract By the magnetically modulated microwave absorption method (MAMMA) we observed the modifications induced by different calcination temperatures (between 830°C and 870°C) on the 2223 phase formed in a system sintered at (855±5)°C with the starting composition Bi1.7Pb0.3Sr2Ca2Cu3O y . The presence of the 2223 phase in almost distinct states (consequently, multiple 2223 phases) in the same sample was observed. As the calcination temperature was increased up to 850°C, the highest temperature state of the 2223 phase intensified. Higher calcination temperatures resulted in the enhancement of other lower-temperature states. The homogeneity of the 2223 phase was greatly improved by annealing the samples at, 800°C for 5 min in a flowing nitrogen atmosphere. We labeled as “metastable” the lower-temperature states having excess oxygen, which, by easily losing the supplementary oxygen under the above annealing procedure, were shifted to higher temperatures.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00727548

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Superconductivity in the cuprates as a consequence of antiferromagnetism and a large hole density of states (1996)

Dagotto, E. ; Nazarenko, A. ; Moreo, A. ; [weitere]

Springer

Journal of superconductivity 9 (1996), S. 379-387

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ISSN: 1572-9605

Schlagwort(e): Superconductivity ; t-J and Hubbard models ; mechanisms

Quelle: Springer Online Journal Archives 1860-2000

Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik

Notizen: Abstract We briefly review a theory for the cuprates that has been recently proposed based on the movement and interaction of holes in antiferromagnetic (AF) backgrounds. A robust peak in the hole density of states (DOS) is crucial to produce a large critical temperature once a source of hole attraction is identified. The predictions of this scenario are compared with experiments. The stability of the calculations after modifying some of the original assumptions is addressed. We find that if the dispersion is changed from an antiferromagnetic band at half-filling to a tight-binding cosk x+cosk y narrow band at 〈n〉=0.87, the main conclusions of the approach remain basically the same i.e., superconductivity appears in the $$d_{x^2 - y^2 } $$ -channel andT c is enhanced by a large DOS. The main features distinguishing these ideas from more standard theories based on antiferromagnetic correlations are here discussed.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00727282

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Charge-transfer in YBa2Cu3O x (1996)

Blackstead, Howard A. ; Dow, John D.

Springer

Journal of superconductivity 9 (1996), S. 563-570

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ISSN: 1572-9605

Schlagwort(e): Superconductivity ; charge transfer ; YBa2Cu3Ox

Quelle: Springer Online Journal Archives 1860-2000

Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik

Notizen: Abstract The charge-transfer hypothesis is shown to be inconsistent with data for YBa2Cu3Ox: (i) The two-step behavior ofT c(x) (with jumps from zero to ≈60 K and then to ≈90 K) is not reflected as a similar, statistically significant two-step behavior in the bond-valence-sum charge of cuprate-plane Cu ions (as once believed), (ii) as a consequence of the law of conservation of charge, the derivatives of the layer charges with respect to oxygen contentx for both the Ba-O layers and the charge-reservoir Cu-O chains have the opposite signs to those predicted, and (iii) the charge-transfer observed for superconducting YBa2Cu3Ox is not sufficient to produce superconductivity, as demonstrated by insulating PrBa2Cu3Ox, which has virtually the same layer charges.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1007/BF00728235

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