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Osquiguil, E., R. Decca, G. Nieva, L. Civale, and F. de la Cruz. "La1.80 Sr0.20 CuO4-delta a clean limit superconductor." Solid State Communications 65, no. 6 (1988): 491–494.
Abstract: The electrical resistivity of the superconductor La1.80Sr0.20Cu04-? has been measured in a wide range of temperatures as a function of oxygen and vacuum heat treatments. The resistivity changes reversibly orders of magnitude with oxygen concentration. There is no sign of saturation at high temperatures, even for samples where the resistivity is increased by heat treatment in vacuum. Using the experimental data and general arguments it is concluded that the ceramic superconductors are high ? materials in the clean limit.
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Sarkar, R., M. Baenitz, J. G. Sereni, and C. Geibel. "29Si NMR study of the heavy fermion system CeRuSi." Journal of Physics: Conference Series 200 (2010): 012173.
Abstract: A recent investigation of the low temperature properties of the paramagnetic heavy fermion system CeRuSi revealed an anomalous decrease of the coefficient C/T below 6 K, indicating a second low energy scale well below the Kondo temperature of about 50 K. We started an investigation of this unusual behavior using the local probe 29Si-NMR. Here a preliminary 29Si field sweep NMR study in the temperature 4.2-200 K is reported. 29Si-NMR powder spectra obtained at 72.9 MHz could be simulated and shift components 29Kab(T) and 29K c(T) were determined. The shift along the basal plane 29Kab(T) shows the expected behavior with a Curie-Weiss dependence at high T merging in a constant value below 15 K. In contrast the shift along the tetragonal axis reveals an anomalous T dependence below 15 K where 29Kc(T) drops by a factor of 2, confirming the presence of a further low T energy scale. We suspect this drop to be related to the anomalous decrease of C/T below 6 K and discuss possible mechanism. © 2010 IOP Publishing Ltd.
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Rumi, G., L. J. Albornoz, P. Pedrazzini, M. I. Dolz, H. Pastoriza, C. J. van der Beek, M. Konczykowski, and Y. Fasano. "Entropy jump at the first-order vortex phase transition in Bi2Sr2CaCu2O8+δ with columnar defects." Materials Today: Proceedings 14 (2019): 30–33.
Abstract: We study the entropy jump associated with the first-order vortex melting transition (FOT) in Bi2Sr2CaCu2O8+δ crystals by means of Hall probe magnetometry. The samples present a diluted distribution of columnar defects (CD) introduced by irradiation with Xe ions. The FOT is detected in ac transmittivity measurements as a paramagnetic peak, the height of which is proportional to the enthalpy difference entailed by the transition. By applying the Clausius-Clapeyron relation, we quantify the evolution of the entropy jump Δs as a function of the FOT temperature, TFOT, in both pristine crystals and crystals with CD. On increasing the density of CD, Δs decreases monotonically with respect to values found in pristine samples. The Δs versus TFOT dependence in the case of pristine samples follows reasonably well the theoretical prediction of dominant electromagnetic coupling for a model neglecting the effect of disorder. The data for samples with a diluted distribution of CD are not properly described by such a theoretical model.
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Navarro, H., M. Sirena, J. Kim, and N. Haberkorn. "Josephson coupling in high-Tc superconducting junctions using ultra-thin BaTiO3 barriers." Materials Science and Engineering: B 262 (2020): 114714.
Abstract: We study the electrical transport of vertically-stacked Josephson tunnel junctions using GdBa2Cu3O7−δ electrodes and a BaTiO3 barrier with thicknesses between 1 nm and 3 nm. Current-voltage measurements at low temperatures show a Josephson coupling for junctions with BaTiO3 barriers of 1 nm and 2 nm. Reducing the barrier thickness bellow a critical thickness seems to suppress the ferroelectric nature of the BaTiO3. The Josephson coupling temperature reduces as the barrier thicknesses increases. The Josephson energies at 12 K are of ≈ 1.5 mV and ≈ 7.5 mV for BaTiO3 barriers of 1 nm and 2 nm, respectively. Fraunhofer patterns are consistent with fluctuations in the critical current due to structural inhomogeneities in the barriers. Our results are promising for the development of Josephson junctions using high-Tc electrodes with energy gaps much higher than those usually present in conventional low-temperature superconductors.
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