Electric field gradients in PrBa2 Cu 3 O 7 : LSDA+U results and comparison with experiment |
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Authors: | V Ghanbarian and M R Mohammadizadeh |
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Institution: | (1) Department of Physics, University of Tehran, Superconductivity Research Laboratory (SRL), P.O. Box 14395, North Karegar Ave., Tehran, Iran;(2) Department of Nano-Science, Institute for Studies in Theoretical Physics and Mathematics (IPM), P.O. Box 19395, Tehran, Iran |
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Abstract: | Electric-field gradient (EFG) and asymmetry parameter (η) at all
oxygen and copper sites of nonsuperconducting PrBa2Cu3O7
(Pr123) compound were calculated using the full-potential
(linearized)-augmented-plane-wave plus local orbitals method. Exchange and
correlation effects were treated by LSDA+U for Cu(3d) and Pr(4f) electrons.
The effects of changing screened Coulomb parameters UPr, UCu1, and
UCu2 on the results were individually studied. The calculated EFG of O2
site is close to the EFG of O3 site at variance with the experimental
result. It was shown that by increasing superconducting holes in O2 and O3
sites the EFG at these sites increase and vice versa. The most famous
theories which have been proposed to explain the suppression of
superconductivity in perfect (without any mis-substitution or other defects)
Pr123 compound are not consistent with the experimental EFG at O2 and O3
sites. By replacing one Pr atom at the Ba site on unit cell of Pr123
(PrBa), it was shown that PrBa mis-substitution reduces the
superconducting holes in both O2 and O3 sites and could be responsible for
the suppuration of superconductivity in Pr123 samples. It is very probable
that the unusual behaviors of experimental EFG at O2 and O3 sites of Pr123
are related to oxygen defects which are produced with PrBa
mis-substitution. |
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Keywords: | 74 25 Jb Electronic structure 74 72 Bk Y-based cuprates 71 15 Mb Density functional theory local density approximation gradient and other corrections 76 60 -k Nuclear magnetic resonance and relaxation |
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