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2000 (2)
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1Author    Detlef BrinkmannRequires cookie*
 Title    Quadrupolar Relaxation -what would we do without it in High-r c Superconductor Studies?  
 Abstract    This paper emphasizes the fact that valuable information on the dynamics of high-T c super-conductors is concealed in that part of the spin-lattice relaxation which arises from quadrupolar interactions. We briefly discuss the problem how to disentangle magnetic and quadrupolar time dependent interactions if both are present, thus leading to multiexponential magnetization recovery laws. We then discuss two examples from our studies of the high-T C superconductor YBaaC^Os where the identification of a quadrupolar contribution to the spin-lattice relaxation has been es-sential to draw the relevant conclusions. One example is concerned with the charge fluctuations associated with an electronic crossover showing up in the oxygen relaxation. The second example is dealing with the separation of charge and spin excitations and the validity of the single-spin fluid model. 
  Reference    Z. Naturforsch. 55a, 323—326 (2000); received August 25 1999 
  Published    2000 
  Keywords    NQR, NMR, Quadrupolar Relaxation, High-Temperature Superconductors 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0323.pdf 
 Identifier    ZNA-2000-55a-0323 
 Volume    55 
2Author    Detlef BrinkmannRequires cookie*
 Title    Spin Gap, Electronic Crossover, and Charge Density Waves in Y-Ba-Cu-O Superconductors  
 Abstract    This paper discusses recent NQR/NMR studies performed on Y-Ba-Cu-0 superconductors at the Uni-versity of Zürich. The work is concerned with normal state properties which are still controversial, for instance the spin-gap effect, i.e. the opening of a pseudo gap in the electron spin excitation spectrum at a temperature 7*, which lies above T c . We will report on the detection of "anomalies" which are dis-played in the temperature dependence of several NMR and NQR quantities measured in the normal state of YBa 2 Cu 4 0 8 . These anomalies are interpreted as an electronic crossover which involves a charge re-distribution in the Cu0 2 planes and an enhancement of the charge fluctuations. As a possible mecha-nism of the crossover, a charge density wave instability is proposed. 
  Reference    Z. Naturforsch. 53a, 488—491 (1998); received December 30 1997 
  Published    1998 
  Keywords    NQR, NMR, High-Temperature Superconductors, Spin gap Electronic Crossover 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0488.pdf 
 Identifier    ZNA-1998-53a-0488 
 Volume    53 
3Author    D. BrinkmannRequires cookie*
 Title    Probing the Electronic Structure of Y-Ba-Cu-O Superconductors by Copper NQR/NMR  
 Abstract    The paper discusses some NQR/NMR studies performed on Y-Ba-Cu-O superconductors at the University of Zürich. It is shown how the resonance methods can yield information on electronic properties of quite different character. The review deals with: (1) the temperature and pressure dependence of Cu NQR frequencies in YBa 2 Cu 4 O g (1-2-4); (2) an NQR study of the properties of Ca substituted 1-2-4; (3) the temperature dependence of the Cu Knight shifts in 1-2-4; (4) the NMR of plane Cu2 in the paramagnetic state of YBa 2 Cu 3 0 6 ; (5) the dependence on temperature, pressure and orientation of the Cu spin-lattice relaxation in 1-2-4. 
  Reference    Z. Naturforsch. 47a, 1—6 (1992); received September 20 1991 
  Published    1992 
  Keywords    NQR, NMR, High-temperature superconductors, Knight shift, Spin-lattice relaxation 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0001.pdf 
 Identifier    ZNA-1992-47a-0001 
 Volume    47 
4Author    D. BrinkmannRequires cookie*
 Title    Inter-plane Coupling and Spin Gap -an NMR/NQR Look on Typical Properties of High-Temperature Superconductors  
 Abstract    The paper discusses some NQR/NMR studies performed on Y-Ba-Cu-O superconductors at the University of Zürich. In particular, we review studies performed in Y 2 Ba 4 Cu 7 0 15 by measuring various planar Cu NQR/NMR parameters: the spin-lattice relaxation time, the Knight shift and the indirect component of the Gaussian contribution to the spin-spin relaxation time. The temperature dependence of these parameters reveals a coupling between adjacent planes of a double plane. The existence of the inter-plane coupling has independently been confirmed by performing NQR Spin-Echo Double Resonance (SEDOR) experiments. The appearance of a spin gap seems to be the consequence of inter-plane coupling. 
  Reference    Z. Naturforsch. 51a, 786—792 (1996); received November 20 1995 
  Published    1996 
  Keywords    NQR, NMR, High-Temperature Superconductors, Inter-plane Coupling, Spin gap 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0786.pdf 
 Identifier    ZNA-1996-51a-0786 
 Volume    51 
5Author    P. F. Meier, T. A. Claxton, P. Hüsser, S. Plibersek, E. P. StollRequires cookie*
 Title    Cluster Calculations of Hyperfine Interactions in Superconducting Copper Compounds  
 Abstract    This paper discusses first-principles cluster investigations on the electronic structure of YBa2Cu3Ü7 and La2CuC>4 performed at the University of Zürich. In particular, electric field gradients have been calculated at the copper sites and their dependence on applying uniaxial strain is studied. Magnetic hyperfine interactions have been evaluated from spin-polarized calculations, and the transfer of spin density from neighboring copper ions is explained. An interpretation is given of the nuclear quadrupole resonance spectra in doped La2CuC>4. 
  Reference    Z. Naturforsch. 55a, 247—255 (2000); received August 26 1999 
  Published    2000 
  Keywords    Cluster Calculations, Electric Field Gradients, High-Temperature Superconductors, Hyperfine Fields, Nuclear Quadrupole Resonance 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0247.pdf 
 Identifier    ZNA-2000-55a-0247 
 Volume    55