| | 1 | Author
| YuA. Ossipyan, O. V. Zharikov, V. L. Matukhin, V. N. Anashkin, I. A. Safin, A. I. Pogorelcev, G. B. Teitelbaum, Yba, Cu, Iodination | Requires cookie* | | | Title
| Cu NQR Study in a High-J c Superconductor YBa 2 Cu 3 0 6A l x  | | | | Abstract
| NQR-spectra and nuclear relaxation of 63 Cu in ceramic samples of the Y-Ba-Cu-O system with various oxygen content have been compared with those in iodinated YBa 2 Cu 3 O eA . | | | |
Reference
| Z. Naturforsch. 47a, 21—26 (1992); received August 8 1991 | | | |
Published
| 1992 | | | |
Keywords
| NQR-spectra, Relaxation, Superconductivity | | | |
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| default:Reihe_A/47/ZNA-1992-47a-0021.pdf | | | | Identifier
| ZNA-1992-47a-0021 | | | | Volume
| 47 | |
| 2 | Author
| W. W. Warren, R. E. Walstedt | Requires cookie* | | | Title
| NQR and NMR Studies of Spin Dynamics in High T c Superconducting Cuprates | | | | Abstract
| Recent NQR and NMR studies of Cu spin dynamics in metallic YBa 2 Cu 3 0 6+JC are reviewed. The Cu nuclear relaxation rates are shown to be inconsistent with weak correlation (band) theory and the Korringa relation, but the Cu spins retain important characteristics of itinerancy. These include pairing of the Cu d-spins in the superconducting state and strong sensitivity of the Cu spin dynamics to changes in carrier concentration associated with variation of the oxygen content. Samples of reduced oxygen content (T c = 60 K) are found to contain a high concentration of Cu + Cu(l) sites associated with "full chain-empty chain" vacancy ordering. These samples also exhibit remarkable precursive suppression of planar Cu(2) nuclear relaxation above T c . | | | |
Reference
| Z. Naturforsch. 45a, 385—392 (1990); received October 25 1989 | | | |
Published
| 1990 | | | |
Keywords
| NMR, NQR, Nuclear relaxation, Spin fluctuations, Superconductivity | | | |
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| default:Reihe_A/45/ZNA-1990-45a-0385.pdf | | | | Identifier
| ZNA-1990-45a-0385 | | | | Volume
| 45 | |
| 3 | Author
| S. Gärtner, H. Riesemeier, Y. Kitaoka, V. Müller, K. Lüders, E. Kaldis, S. Rusiecki | Requires cookie* | | | Title
| Cu-NQR Frequencies and Linewidths in High-T c Superconductors | | | | Abstract
| The Cu-NQR lines of various high-T c superconductors at the Cu(2) site appear between 15 and 40 MHz. There exists an experimental correlation showing that the NQR frequency increases with decreasing T c . By comparison, it can be concluded from these results that a formal valence state of the Cu ion around 2 + is favourable for superconductivity. All lines exhibit a strong broadening compared to Cu0 2 crystals, which is attributed to lattice modulations within the Cu0 2 layers. This effect also influences the temperature dependence of the linewidth in YBa 2 Cu 3 0 7 _ a . | | | |
Reference
| Z. Naturforsch. 47a, 27—29 (1992); received August 3 1991 | | | |
Published
| 1992 | | | |
Keywords
| NQR, Superconductivity, High-T c compounds, Resonance frequency, Linewidth | | | |
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| default:Reihe_A/47/ZNA-1992-47a-0027.pdf | | | | Identifier
| ZNA-1992-47a-0027 | | | | Volume
| 47 | |
| 5 | Author
| MichaelC. Böhm, Christoph Saal | Requires cookie* | | | Title
| On a Direct Superconducting Pairing Mechanism | | | | Abstract
| We suggest that superconductivity can be traced back to a first-order interaction between the charge carriers which does not necessarily involve second-order electron-phonon coupling. For small molecular model systems it is demonstrated that the formation of Cooper pairs can lead to an attenuation of the destabilizing influence of the Pauli antisymmetry principle (PAP). We suggest that this attenuation of a fermionic quantum constraint is the driving force for the superconducting transition. Whenever the PAP is activated in single-particle hoppings of electrons, the corresponding moves reduce the electronic derealization; they raise the ensemble energy. The stability of a fermionic system is enhanced with decreasing influence of the PAP. Moves of Cooper pairs are not influenced by any quantum constraint of the intersite type. This behaviour differs from the well-known fermionic constraints. The quantum statistics of Cooper pairs is of a mixed type combining a fermionic on-site and a bosonic intersite behaviour. It coincides with the quantum statistics of so-called hard core bosonic ensembles. In the present work Cooper pair formation has been studied for smaller molecular models. The electronic Hamiltonian employed is of the two-parameter Hubbard-type. The solid state phenomenon superconductivity is correlated with the molecular concepts of "antiaromaticity" and "aromaticity". Arguments are given which support the present interpretation. | | | |
Reference
| Z. Naturforsch. 54a, 718—738 (1999); received May 26 1999 | | | |
Published
| 1999 | | | |
Keywords
| Superconductivity, Possible First-Order Pairing Interaction, Quantum Statistics, Pauli Antisymmetry Principle, Superconductivity vs Antiaromaticity and Aromaticity | | | |
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| default:Reihe_A/54/ZNA-1999-54a-0718.pdf | | | | Identifier
| ZNA-1999-54a-0718 | | | | Volume
| 54 | |
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