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Janusz Andrzej Karpinski
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Domaines de recherche associés (20)
Supraconducteur à haute température
Un supraconducteur à haute température (en anglais, high-temperature superconductor : high- ou HTSC) est un matériau présentant une température critique de supraconductivité relativement élevée par r
Supraconductivité
La supraconductivité, ou supraconduction, est un phénomène physique caractérisé par l'absence de résistance électrique et l'expulsion du champ magnétique — l'effet Meissner — à l'intérieur de certains
Monocristal
Un monocristal ou matériau monocristallin est un matériau solide constitué d'un unique cristal, formé à partir d’un seul germe. À l'opposé, un polycristal ou matériau polycristallin, est constitué
Publications associées (29)
Local lattice distortions vs. structural phase transition in NdFeAsO1-xFx
Janusz Andrzej Karpinski, Sergiy Katrych
The lattice properties at low temperatures of two samples of NdFeAsO1-xFx (x = 0.05 and 0.25) have been examined in order to investigate possible structural phase transition that may occur in the optimally doped superconducting sample with respect to the non-superconducting low-F concentration compound. In order to detect small modifications in the ion displacements with temperature micro-Raman and high resolution synchrotron powder diffraction measurements were carried out. No increase of the width of the (2 2 0) or (3 2 2) tetragonal diffraction peaks and microstrains could be found in the superconducting sample from synchrotron XRD measurements. On the other hand, the atomic displacement parameters deviate from the expected behavior, in agreement with modifications in the phonon width, as obtained by Raman scattering. These deviations occur around 150 K for both F dopings, with distinct differences among the two compounds, i.e., they decrease at low doping and increase for the superconducting sample. The data do not support a hidden phase transition to an orthorhombic phase in the superconducting compound, but point to an isostructural lattice deformation. Based on the absence of magnetic effects in this temperature range for the superconducting sample, we attribute the observed lattice anomalies to the formation of local lattice distortions that, being screened by the carriers, can only acquire long-range coherence by means of a structural phase transition at low doping levels. (C) 2016 Elsevier B.V. All rights reserved.
Elsevier2016Magnetotransport studies of superconducting Pr4Fe2As2Te1-xO4
László Forró, Richard Gaal, Janusz Andrzej Karpinski, Sergiy Katrych, Bálint Náfrádi, Andrea Pisoni, Péter Szirmai
We report a study of the electrical transport properties of single crystals of Pr(4)Fe(2)As(2)Te(1-)xO(4), a recently discovered iron-based superconductor. Resistivity, Hall effect, and magnetoresistance are measured in a broad temperature range revealing the role of electrons as dominant charge carriers. The significant temperature dependence of the Hall coefficient and the violation of Kohler's law indicate multiband effects in this compound. The upper critical field and the magnetic anisotropy are investigated in fields up to 16 T, applied parallel and perpendicular to the crystallographic c axis. Hydrostatic pressure up to 2 GPa linearly increases the critical temperature and the resistivity residual ratio. A simple two-band model is used to describe the transport and magnetic properties of Pr4Fe2As2Te1-xO4. The model can successfully explain the strongly temperature-dependent negative Hall coefficient and the high magnetic anisotropy, assuming that the mobility of electrons is higher than that of holes.
Amer Physical Soc2016Single crystals of superconducting SmFeAsOHx: Structure and properties
Alla Arakcheeva, László Forró, Richard Gaal, Ping Huang, Janusz Andrzej Karpinski, Sergiy Katrych, Péter Krisztián Matus, Andrea Pisoni
We report the synthesis, structure, and superconducting properties of single crystals of SmFeAsOHx. The crystals were grown at high pressure and high temperature using a cubic anvil technique. H-1-NMR studies confirm the presence of H atoms in the samples. Single crystal x-ray diffraction analyses demonstrate a remarkable disorder in the Sm2O2 layers induced by hydrogen incorporation and reveal that the H positions are compatible with a H2O-like geometry inside the crystals. We have measured the magnetotransport properties of SmFeAsOHx single crystals with x = 0.07, 0.11, and 0.16 in magnetic field up to 16 T, oriented along the two main crystallographic directions. The results show an increase of the critical temperature with hydrogen content. The zero-temperature upper critical fields and the magnetic anisotropy are calculated as a function of the hydrogen content. SmFeAsOHx crystals present significantly higher upper critical fields and magnetic anisotropies compared to SmFeAsO1-x F-x compounds.
Amer Physical Soc2016Personnes menant des recherches similaires (91)