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Register a new userCritical current density in the superconducting ceramic $rm La_{1.8}Sr_{0.2}CuO_4$ in S-c-N point contacts
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Measurement of the current-voltage characteristics of point contacts makes it possible to study the properties of individual crystallites in a superconducting ceramic. The critical current density in the superconducting regions of the ceramic $rm La_{1.8}Sr_{0.2}CuO_4$, with a size of the order of several tens of angstroms, is found to attain values of $10^8 A/cm^2$, which are of the same order of magnitude as the pair-breaking current density, as evaluated from the formulas of the standard theory of superconductivity.
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We report Cu and La nuclear magnetic resonance (NMR) measurements in the title compound that reveal an inhomogeneous glassy behavior of the spin dynamics. A low temperature peak in the La spin lattice relaxation rate and the ``wipeout of Cu intensity both arise from these slow electronic spin fluctuations that reveal a distribution of activation energies. Inhomogeneous slowing of spin fluctuations appears to be a general feature of doped lanthanum cuprate.
$mathrm{La_{1.85}Sr_{0.15}CuO_4}$/$mathrm{La_2CuO_4}$ (LSCO15/LCO) bilayers with a precisely controlled thickness of N unit cells (UCs) of the former and M UCs of the latter ([LSCO15_N/LCO_M]) were grown on (001)-oriented {slao} (SLAO) substrates with pulsed laser deposition (PLD). X-ray diffraction and reciprocal space map (RSM) studies confirmed the epitaxial growth of the bilayers and showed that a [LSCO15_2/LCO_2] bilayer is fully strained, whereas a [LSCO15_2/LCO_7] bilayer is already partially relaxed. The textit{in situ} monitoring of the growth with reflection high energy electron diffraction (RHEED) revealed that the gas environment during deposition has a surprisingly strong effect on the growth mode and thus on the amount of disorder in the first UC of LSCO15 (or the first two monolayers of LSCO15 containing one $mathrm{CuO_2}$ plane each). For samples grown in pure $mathrm{N_2O}$ gas (growth type-B), the first LSCO15 UC next to the SLAO substrate is strongly disordered. This disorder is strongly reduced if the growth is performed in a mixture of $mathrm{N_2O}$ and $mathrm{O_2}$ gas (growth type-A). Electric transport measurements confirmed that the first UC of LSCO15 next to the SLAO substrate is highly resistive and shows no sign of superconductivity for growth type-B, whereas it is superconducting for growth type-A. Furthermore, we found, rather surprisingly, that the conductivity of the LSCO15 UC next to the LCO capping layer strongly depends on the thickness of the latter. A LCO capping layer with 7~UCs leads to a strong localization of the charge carriers in the adjacent LSCO15 UC and suppresses superconductivity. The magneto-transport data suggest a similarity with the case of weakly hole doped LSCO single crystals that are in a so-called {{cluster-spin-glass state}}
We present La and Cu NMR relaxation measurements in single crystal La_{1.67}Eu_{0.2}Sr_{0.13}CuO_4. A strong peak in the La spin-lattice relaxation rate observed in the spin ordered state is well-described by the BPP mechanism[1] and arises from continuous slowing of electronic spin fluctuations with decreasing temperature; these spin fluctuations exhibit XY-like anisotropy in the ordered state. The spin pseudogap is enhanced by the static charge-stripe order in the LTT phase.
Low temperature specific heat of the electron-doped (n-type) infinite-layer cuprate $Sr_{0.9}La_{0.1}CuO_{2}$ has been measured. The quasiparticle density of states (DOS) in the mixed state is found to be consistent with the feature of the s-wave pairing symmetry, agreeing very well with the earlier tunnelling measurement, but being contrary to the d-wave symmetry well confirmed for the hole-doped (p-type) cuprates. Our results indicate that the electronic DOS are mainly contributed by the vortex cores in the present sample being contrast to the p-type cuprates in which the vortex cores are abnormal and contribute very limited low energy DOS as evidenced by many means.
Using Ta, 2H-NbSe2 and MgB2 as an example it is shown that it is possible to reconstruct qualitatively a function of the electron-phonon interaction from point-contact spectra in a superconducting state. The limits and the restrictions of this method are also shown. The results obtained are compared with available literature data.
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