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In this paper it is reported that the measurement of the bulk positron lifetime as a function of substitution content x in the temperature range from 70 to 220K was performed in two high-Tc superconducting systems, Y1-xCaxBa2Cu3-xFexO7-δ and Y1-xCaxBa2Cu3O7-δ. It was found that τB of both systems decreases significantly with x and the temperature dependence of τB is very weak in normal state. In lower temperature region (Tc), a dramatic x-dependent temperature variation of τB was observed in the Ca-substituted system: from a decrease of τB with decreasing T to an increase of τB. With increasing x, the temperature dependence of τB remains weak in the Ca- and Fe- substituted systems. Compared with the experimental data of positron lifetime in other substituted systems and the calculation of the positron density distribution, the authors suggest that positron bulk lifetime spectra behaviour can be interpreted by the physical model based on the transfer of electron density between the CuO2 planes and Cu-O chains. Therefore, the study of positron lifetime spectra provides a useful means to detect the local charge density and to study the correlation between the electronic structure and the high-Tc superconductivity. 相似文献
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E. B. Amitin A. G. Baikalov A. G. Blinov L. A. Boyarskii V. Ya. Dikovskii K. R. Zhdanov M. Yu. Kameneva L. P. Kozeeva A. P. Shelkovnikov 《JETP Letters》1999,70(5):352-357
The magnetoresistance of lightly doped TmBa2Cu3Ox single crystals is investigated in the temperature range 4.2–300 K for magnetic fields up to 12 T. For the antiferromagnetic
sample (x=6.3), when the current and field lie in the ab plane, the magnetoresistance is the sum of an anisotropic and a background component. The existence of the anisotropic component
is attributed to the restructuring of the antiferromagnetic domain structure in a magnetic field.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 5, 350–355 (10 September 1999) 相似文献
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《Physics letters. A》1987,125(4):222-224
The susceptibility anomaly observed at 13 K for Y2Cu2O5 strongly suggests the occurrence of antiferromagnetic Cu spin coupling in this compound. Only paramagnetic behaviour was found for BaCuO2. 相似文献
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P. Boolchand D. McDaniel C. Blue Y. Wu R. Enzweiler K. Elgaid R. Burrows 《Hyperfine Interactions》1992,68(1-4):15-25
A new symmetric Fe3+ site (labelled E) (δ=0.28(2) mm/s and Δ=0.15 mm/s) is observed in the R1Ba2Cu3O7 family of superconductors for R=Y and Eu. The decay and growth of site E are established in two seemingly unrelated experiments,
one as a function of room temperature aging for R=Y, and the other as a function of oxygen loading at elevated temperatures
and pressures for R=Eu. In each experiment, the results show that site E is genetically related to the well documented chainsites
A(Δ=1.9 mm/s), C(Δ=1.1 mm/s) and D(Δ=1.6 mm/s). We propose that site E represents a quasi-octahedral chain-site having pairs
of O(1), O(4) and O(5) nearestneighbor oxygen sites. The two remaining doublets, B(Δ≈0.4 mm/s) and B′(Δ=0.78 mm/s) represent
Fe3+ dopant sites present in the all-important CuO2 planes, possessing coordination numbers of 6 and 5, respectively. 相似文献
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The characteristic d-type angular dependence of the in-plane magnetoresistance on the orientation of the external magnetic field in the (ab) plane for the antiferromagnetic tetragonal crystal YBa2Cu3O6+x (x ~ 0.3) is considered theoretically. This dependence is interpreted in terms of the efficient hole transfer through the low-lying purely oxygen O 2pe u doublet, which is not hybridized with the $b_{1g} (d_{{}_x2_ - {}_y2} )$ ground state. The external magnetic field determines the orientation of the strong exchange field acting on the b 1g e u : 3 E u triplet state of the hole-type CuO4 center. The spin-orbit interaction results in orbital polarization of the E u doublet, which is responsible for the d-type spatial anisotropy of the hole transport. The available experimental data make it possible to evaluate the parameter of the effective spin Hamiltonian. The influence of spin-vibronic effects on the hole transfer is analyzed. 相似文献
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Ch. Niedermayer C. Bernhard T. Blasius A. Decker A. Golnik 《Hyperfine Interactions》1997,105(1-4):131-137
We have studied the magnetic phase diagram for the bilayer compound Y1-x Cax Ba2 Cu3 O6 in the regime of low doping (hole concentration within a CuO2 plane, psh < 0.1). For psh < 0.03, the data demonstrate the freezing of the spin degrees of freedom associated with the doped holes into a spin‐glass‐like
state which is superimposed on the preexisting long range order of the Cu2+ spins. Only a single spin‐glass like transition at a temperature Tg is observed for samples in the hole concentration range 0.03 < psh < 0.1. While the threshold for the occurrence of superconductivity is almost the same (psh > 0.06) for the Y1-x Cax Ba2 Cu3 O6 and the La2-x Srx CuO4 systems, the magnetic correlations that coexist with superconductivity are considerably stronger in the bilayer Y1-x Cax Ba2 Cu3 O6 system as indicated by significantly increased transition temperatures Tg.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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