650 research outputs found
Universal observation of multiple order parameters in cuprate superconductors
The temperature dependence of the London penetration depth \lambda was
measured for an untwined single crystal of YBa_2Cu_3O_{7-\delta} along the
three principal crystallographic directions (a, b, and c). Both in-plane
components (\lambda_a and \lambda_b) show an inflection point in their
temperature dependence which is absent in the component along the c-direction
(\lambda_c). The data provide convincing evidence that the in-plane
superconducting order parameter is a mixture of s+d-wave symmetry whereas it is
exclusively s-wave along the c-direction. In conjunction with previous results
it is concluded that coupled s+d-order parameters are universal and intrinsic
to cuprate superconductors.Comment: 5 pages, 3 figure
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It is established that the average (over the number of bonds) intensity of the superexchange interaction of the Fe**3** plus ion with magnetic neighbors decreases by 10% on replacement of one oxygen ion with a fluorine ion, irrespective of the nature of the cation substitution
Isotope effect on the transition temperature in Fe-based superconductors: the current status
The results of the Fe isotope effect (Fe-IE) on the transition temperature
obtained up to date in various Fe-based high temperature superconductors
are summarized and reanalyzed by following the approach developed in [Phys.
Rev. B 82, 212505 (2010)]. It is demonstrated that the very controversial
results for Fe-IE on are caused by small structural changes occurring
simultaneously with the Fe isotope exchange. The Fe-IE exponent on
[, is the isotope mass]
needs to be decomposed into two components with the one related to the
structural changes () and the genuine (intrinsic)
one (). The validity of such decomposition is
further confirmed by the fact that coincides with
the Fe-IE exponent on the characteristic phonon frequencies as is reported in recent EXAFS and Raman experiments.Comment: 7 pages, 4 figures. The paper is partially based on the results
published in [New J. Phys. 12, 073024 (2010) = arXiv:1002.2510] and [Phys.
Rev. B 82, 212505 (2010) = arXiv:1008.4540
Iron isotope effect on the superconducting transition temperature and the crystal structure of FeSe_1-x
The Fe isotope effect (Fe-IE) on the transition temperature T_c and the
crystal structure was studied in the Fe chalcogenide superconductor FeSe_1-x by
means of magnetization and neutron powder diffraction (NPD). The substitution
of natural Fe (containing \simeq 92% of ^{56}Fe) by its lighter ^{54}Fe isotope
leads to a shift of T_c of 0.22(5)K corresponding to an Fe-IE exponent of
\alpha_Fe=0.81(15). Simultaneously, a small structural change with isotope
substitution is observed by NDP which may contribute to the total Fe isotope
shift of T_c.Comment: 4 pages, 3 figure
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