1,784 research outputs found
Nernst effect in single crystals of the pnictide superconductor CaFe1.92Co0.08As2 and parent compound CaFe2As2
We report a combined study of the Nernst coefficient (v), Hall effect and
thermoelectric power of CaFe2As2 and CaFe1.92Co0.08As2 single crystals. The
absolute value of v in both samples is enhanced, probably due to ambipolar flow
of electron- and hole-like quasiparticles. The onset of spin-density-wave order
in CaFe2As2 causes further rapid rise of the Nernst coefficient. On the
contrary, in the CaFe1.92Co0.08As2 crystal we do not see any feature of v(T),
which could be clearly associated with SDW fluctuations. In this Co-doped
sample there is also no noticeable increase in of v in the vicinity of
superconducting transition, despite the expectation of such due to vortex
movement.Comment: 6 pages, 3 figures; (v2) slight changes and clarifications; to appear
in Phys. Rev.
Multi-band superconductivity in LaFeAsO_{0.9}F_{0.1} single crystals probed by high-field vortex torque magnetometry
To probe manifestations of multiband superconductivity in oxypnictides, we
measured the angular dependence of the magnetic torque in the
mixed state of LaOFFeAs single crystals as a function of
temperature and magnetic fields up to 18 T. The paramagnetic
contribution of the Fe ions is properly treated in order to extract the
effective mass anisotropy parameter from
. We show that depends strongly on both and ,
reaching a maximum value of 10 followed by a decrease towards values
close to 1 as is lowered. The observed field dependencies of the London
penetration depth and suggest the onset of suppression
of a superconducing gap at .Comment: 7 pages, 7 figure
Re-entrance of resistivity due to the interplay of superconductivity and magnetism in \ce{Eu_{0.73}Ca_{0.27}(Fe_{0.87}Co_{0.13})2As2}
By simultaneous Co and Ca-doping we were able to obtain an
\ce{EuFe2As2}-based compound with superconductivity appearing above the
antiferromagnetic order of \ce{Eu^{2+}} magnetic moments. However, as soon as
the antiferromagnetic order appears a re-entrance behavior is observed
\textemdash{} instead of zero resistivity and diamagnetic signal down to the
temperature of \unit[2]{K}. By investigating magnetization, ac susceptibility
and electrical transport properties of
\ce{Eu_{0.73}Ca_{0.27}(Fe_{0.87}Co_{0.13})2As2} and comparing them to
previously studied M\"ossbauer effect and neutron scattering measurements of
this and similar compounds an explanation of such behavior is proposed.Comment: Main paper of 9 pages with 9 figures with Supplementary Material
3D-xy critical properties of YBa2Cu4O8 and magnetic field induced 3D to 1D crossover
We present reversible magnetization data of a YBa2Cu4O8 single crystal and
analyze the evidence for 3D-xy critical behavior and a magnetic field induced
3D to 1D crossover. Remarkable consistency with these phenomena is observed in
agreement with a magnetic field induced finite size effect, whereupon the
correlation length transverse to the applied magnetic field cannot grow beyond
the limiting magnetic length scale L_H. By applying the appropriate scaling
form we obtain the zero-field critical temperature, the 3D to 1D crossover, the
vortex melting line and the universal ratios of the related scaling variables.
Accordingly there is no continuous phase transition in the (H,T)-plane along
the H_c2-lines as predicted by the mean-field treatment.Comment: 8 pages, 4 figure
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