5 research outputs found
First-Principles Calculation of Electric Field Gradients and Hyperfine Couplings in YBa2Cu3O7
The local electronic structure of YBa2Cu3O7 has been calculated using
first-principles cluster methods. Several clusters embedded in an appropriate
background potential have been investigated. The electric field gradients at
the copper and oxygen sites are determined and compared to previous theoretical
calculations and experiments. Spin polarized calculations with different spin
multiplicities have enabled a detailed study of the spin density distribution
to be made and a simultaneous determination of magnetic hyperfine coupling
parameters. The contributions from on-site and transferred hyperfine fields
have been disentangled with the conclusion that the transferred spin densities
essentially are due to nearest neighbour copper ions only with marginal
influence of ions further away. This implies that the variant temperature
dependencies of the planar copper and oxygen NMR spin-lattice relaxation rates
are only compatible with commensurate antiferromagnetic correlations. The
theoretical hyperfine parameters are compared with those derived from
experimental data.Comment: 14 pages, 12 figures, accepted to appear in EPJ
Planar Cu and O hole densities in high-Tc cuprates determined with NMR
The electric hyperfine interaction observable in atomic spectroscopy for O
and Cu ions in various configurations is used to analyze the quadrupole
splitting of O and Cu nuclear magnetic resonance (NMR) in La2-xSrxCuO4 and
YBa2Cu3O6+y and to determine the hole densities at both sites as a function of
doping. It is found that in La2-xSrxCuO4 all doped holes (x) reside in the Cu-O
plane but almost exclusively at O. For YBa2Cu3O6+y and y<0.6 doped holes are
found at planar Cu as well as O. For y>0.6 further doping increases the hole
content only for planar O. The phase diagram based on NMR data is presented.
Further implications from the Cu A and B site in La2-xSrxCuO4 and the two
planar O sites in YBa2Cu3O6+y and consequences for the phase diagram are
discussed.Comment: 18 pages, 1 figure, 2 tables, 2 appendice