74 research outputs found
Critical currents and pinning forces in Nd2−xCexCuO4− thin films
Critical current density, Jc, and flux-pinning force density, Fp, have been investigated at different temperatures
in electron-doped Nd2−xCexCuO4− thin films for magnetic fields, H, applied parallel to the c axis. The
reduced pinning force density fFp /Fp
max shows a clear scaling behavior when H is normalized to the
irreversibility field H, indicating the presence of the same pinning mechanism in the investigated temperature
range. Moreover the maximum of Fp as function of the field at each temperature depends linearly on H. The
experimental data, interpreted using a modified Anderson-Kim description of the flux-creep theory, imply a
magnetic field dependence of the activation energy UHH− with =0.8. This value indicates that in
Nd2−xCexCuO4− a quasi-two-dimensional vortex system is present, intermediate between Bi-based and
Y-based hole-doped compounds
Dirac surface states, multiorbital dimerization and superconductivity in Nb- and Ta-based A15 compounds
Using first-principle calculations, we investigate the electronic,
topological and superconducting properties of NbX (X = Ge, Sn, Sb) and
TaY (Y = As, Sb, Bi) A15 compounds. We demonstrate that these compounds
host Dirac surface states which are related to a nontrivial Z topological
value. The spin-orbit coupling (SOC) splits the eightfold degenerate R point
close to the Fermi level enhancing the amplitude of the spin Hall conductance.
Indeed, despite the moderate spin-orbit of the Nb-compounds, a large spin Hall
effect is also obtained in NbGe and NbSn compounds. We show that the
Coulomb interaction opens the gap at the R point thus making more evident the
occurrence of Dirac surface states. We then investigate the superconducting
properties by determining the strength of the electron-phonon BCS coupling. The
evolution of the critical temperature is tracked down to the 2D limit
indicating a reduction of the transition temperature which mainly arises from
the suppression of the density of states at the Fermi level. Finally, we
propose a minimal tight-binding model based on three coupled
Su-Schrieffer-Heeger chains with t Ta- and Nb-orbitals reproducing the
spin-orbit splittings at the R point among the -bond bands in this class
of compounds. We separate the kinetic parameters in and -bonds,
in intradimer and interdimer hoppings and discuss their relevance for the
topological electronic structure. We point out that NbGe might represent a
Z topological metal with the highest superconducting temperature ever
recorded.Comment: 16 pages, 12 figures in main text, 3 figures in appendix, Paper
submitted to Physical Review
Critical temperature of triplet superconductor-ferromagnet bilayers as a probe for pairing symmetry
Identifying superconducting materials with spin-polarized Cooper pairs is an
important objective both for exploration of new fundamental physics and for
cryogenic applications in spintronics and quantum sensing. We here compute the
critical temperature of the superconducting transition in a bilayer
comprised of a superconductor with an intrinsic spin-triplet order parameter
and a ferromagnet. We determine how varies both with the thickness of the
ferromagnet and its magnetization direction. We show that both the orbital and
spin part of the triplet superconducting order parameter leave clear signatures
in which do not appear in a bilayer of a conventional s-wave
superconductor and a ferromagnet. In particular, the dependence of on
these variables changes depending on whether or not the superconducting order
parameter features Andreev bound-states and also changes qualitatively when the
magnetization is rotated in the plane of the ferromagnetic film. Measurements
of in such bilayers are therefore useful to identify the pairing symmetry
of intrinsic triplet superconductors
Quasiparticles energy relaxation times in NbN/CuNi nanostripes from critical velocity measurements
The dynamic instability of the moving vortex lattice at high driving currents in NbN/CuNi-based and NbN nanostripes designed for optical detection has been studied. By applying the model proposed by Larkin and Ovchinnikov [Zh. Eksp. Teor. Fiz. 68, 1915 (1975)], from the critical velocity v∗ for the occurrence of the instability, it was possible to estimate the values of the quasiparticle relaxation times τE. The results show that the NbN/CuNi-based devices are characterized by shorter values of τE compared to that of NbN
Local characterization of ferromagnetic properties in ferromagnet/superconductor bilayer by Point Contact Andreev Reflection Spectroscopy
We realized point contact spectroscopy experiment on
ferromagnet/superconductor bilayers. Differential conductance curves show
several features that we explained within Bogoliubov-de Gennes formalism
considering the presence of two interfaces in the
normal-metal-tip/ferromagnet/superconductor device. We demonstrate that such
configuration is suitable as local probe of the spin polarization and thickness
of ferromagnetic layer, directly on bilayer areas. This is due to the high
sensitivity of the Andreev surface states to the physical properties of the
ferromagnetic interlayer
Temperature dependence of resistivity of porous silicon formed on N-substrates
Results of measurement of resistivity of mesoporous silicon formed on n-type substrates in a wide temperature range are presented. Measurements show that at low temperatures there is a growth of resistance of four orders of magnitude compared to that at
room temperature which occurs in a relatively narrow temperature range.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2063
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Magnetotransport and magnetic properties of amorphous NdNi 5 thin films
Abstract: NdNi5 is an intermetallic compound with a bulk Curie temperature (TCurie) of 6–13 K. While existing studies have focused on NdNi5 crystals, amorphous thin-films of NdNi5 are potentially important since they would be magnetically soft without magnetocrystalline anisotropy, meaning that small external magnetic fields could reverse the direction of their magnetization. Here, we report NdNi5 thin-films with a thickness in the 5–200 nm range, deposited by DC magnetron sputtering onto Si(100). Films are amorphous with a weak temperature-dependent resistivity with values ranging between 150 and 300 μΩ cm. By means of noise spectroscopy, by analyzing the time-dependence of fluctuation-induced voltages, it is found that at low temperatures the resistance fluctuations are due to the Kondo effect. Volume magnetometry indicates TCurie=70 K with a magnetic coercive field of 30 mT at 5 K for a 125-nm-thick film. The results are promising for the development of Ferromagnet(F)/Superconductor(S)/Ferromagnet(F) pseudo spin-valve devices based on amorphous NdNi5 thin films
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Magnetotransport and magnetic properties of amorphous [Formula: see text] thin films.
[Formula: see text] is an intermetallic compound with a bulk Curie temperature ([Formula: see text]) of 6-13 K. While existing studies have focused on [Formula: see text] crystals, amorphous thin-films of [Formula: see text] are potentially important since they would be magnetically soft without magnetocrystalline anisotropy, meaning that small external magnetic fields could reverse the direction of their magnetization. Here, we report [Formula: see text] thin-films with a thickness in the 5-200 nm range, deposited by DC magnetron sputtering onto Si(100). Films are amorphous with a weak temperature-dependent resistivity with values ranging between 150 and 300 [Formula: see text] cm. By means of noise spectroscopy, by analyzing the time-dependence of fluctuation-induced voltages, it is found that at low temperatures the resistance fluctuations are due to the Kondo effect. Volume magnetometry indicates [Formula: see text] K with a magnetic coercive field of 30 mT at 5 K for a 125-nm-thick film. The results are promising for the development of Ferromagnet(F)/Superconductor(S)/Ferromagnet(F) pseudo spin-valve devices based on amorphous [Formula: see text] thin films
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