Civale, L., H. Pastoriza, F. de la Cruz, J. Guimpel, G. Nieva, J. M. Heintz, O. Durmeyer, and J. P. Kappler. "Meissner fraction of insulating samples of oxide superconductors." Solid State Communications 72, no. 4 (1989): 341–344.
Abstract: The tendency towards superconducting granularity with sample degradation is a common feature of oxide superconductors. We present magnetic, transport and calorimetric results in LiTi$2Ο4$ which show that the topological tendency to segregate the superconducting state into islands surrounded by thin insulating layers is related to the structure of the material rather than to a mechanism associated to high T$_C$. We emphasize that insulating samples with small Meissner fraction can have a superconducting volume fraction close to unity.
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Fasano, Y., M. de Seta, M. Menghini, H. Pastoriza, and F. de la Cruz. "Imaging the structure of the interface between symmetries interconnected by a discontinuous transition." Solid State Communications 128, no. 3-4 (2003): 51–55.
Abstract: We have been able to observe with single particle resolution the interface between two structural symmetries that cannot be interconnected by a continuous transition. By means of an engineered 2D potential that pins the extremity of vortex strings a square symmetry was imposed at the surface of a 3D vortex solid. Using the Bitter decoration technique and on account of the continuous vortex symmetry, we visualize how the induced structure transforms along the vortex direction before changing into the expected hexagonal structure at a finite distance from the surface.
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Herbsommer, J. A., V. F. Correa, G. Nieva, H. Pastoriza, and J. Luzuriaga. "Vortex dynamics in Bi2Sr2CaCu2O8+δ single crystals with planar defects." Solid State Communications 120, no. 2-3 (2001): 59–63.
Abstract: We have studied the effects of c-axis correlated planar defects on the vortex lattice of Bi$2$Sr$2$CaCu$2Ο8$ single crystals using Bitter decoration, transverse ac permeability and X-ray measurements. Our results show that the low field low temperature phase coherent vortex lattice exhibits anisotropic pinning in the presence of these planar defects. Frequency dependent ac permeability measurements show that the ordered solid-liquid transition is first order as in samples free of correlated defects. However, the melting point is detected only when the excitation field is along the defects.
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Shalóm, D. E., and H. Pastoriza. "Experimental evidence for anisotropic response of a driven vortex lattice." Solid State Communications 126, no. 7 (2003): 379–383.
Abstract: We present kinetic inductance measurements in current driven Josephson junction arrays. Measurements performed with circular coils indicate that this technique is very sensitive to the vortex mobility. Results obtained with anisotropic detection coils provide experimental evidence for the anisotropic response of a driven vortex lattice. Anisotropic behavior is obtained when rising the temperature or the mean vortex velocity as indicated by the loss of the superconducting shielding capability, first in the direction of vortex motion and then in the perpendicular direction.
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Trovarelli, O., P. Stickar, J. G. Sereni, G. Schmerber, and J. P. Kappler. "Coexistence of magnetic and non magnetic states in Ce14X51 (X = Au, Ag and Cu)." Solid State Communications 89, no. 5 (1994): 421–424.
Abstract: Magnetic (chi), thermal(C-p), and transport (p) measurements on Ce(l4)X(51) (X = Au, Ag and Cu) are presented. All these compounds show antiferromagnetic type order at low temperatures, with T-N = 0.9 K (Au), 1.1 K (Ag) and 3.2 K (Cu). Within the Gd14Ag51-type structure the Ce atoms sit in different sublattices denoted by I (2 atoms), II (6 atoms) and III (6 atoms), therefore the results can be interpreted in terms of three different behaviors of Ce depending on its local environment. From the entropy involved in the magnetically ordered (MO) phase it can be established that the Ce-II and Ce-III atoms order in Cel4Au51 and Ce14Ag51, while the Ce-I order in Cel4Cu51. There is a large linear contribution to Cp at T > T-N,T-gamma HT = 0.81 (Au), 1.24 (Ag) and 3.1 (Cu) J/mol K-2, which indicates the coexistence of MO and heavy fermions. In the case of Cel4Cu51, the magnetic contribution to Cp from sublattice Ce-I around T-N,T- resembles that of a modulated system and the characteristic temperatures for Ce-II and Ce-III atoms are estimated from p(T) as:T-K=16 K and >120 K respectively.
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Huber, J. G., J. B. Bulman, and J. G. Sereni. "Superconductivity under pressure and low temperature specific heat of ThPr alloys." Solid State Communications 43, no. 12 (1982): 925–931.
Abstract: Measurements of superconducting transition temperature under pressure and low temperature specific heat are presented for ThPr alloys. At 18.2 kbar the normal- to superconducting-state phase boundary extends beyond 50 at.% Pr. This system is discussed in terms of a non-magnetic singlet ground state for the Pr3+ ions due to crystal field splitting. A splitting scheme which varies with Pr concentration is proposed.
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Sereni, J. G., T. E. Huber, and C. A. Luengo. "Low temperature specific heat of Th-Gd spin glass." Solid State Communications 29, no. 9 (1979): 671–673.
Abstract: The specific heat measurements of Th---Gd alloys, with Gd concentration ranging from 0.15% to 10.8% and temperatures between 0.4 and 8 K, are reported. The characteristic spin glass specific heat enhancement and its maximum was found linearly proportional to Gd concentration. At low temperatures a T2 dependence of the specific heat was observed and the entropy associated with the magnetic ordering was the 70% of the expected value for the spin S = 7/2.
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Sereni, J. G., J. G. Huber, C. A. Luengo, and M. B. Maple. "Specific heat of superconducting Th, Sc and Th, Y alloys with Ce." Solid State Communications 17, no. 12 (1975): 1581–1583.
Abstract: Measurements of the specific heat jump ΔC at the superconducting critical temperature Tc on (Image )Ce and (Image )Ce Ce impurity, solid solution alloy systems indicate that the former systems obey the BCS law of corresponding states (LCS) characteristic of superconductors with non-magnetic impurities while the latter systems present deviations from the LCS linear relation between reduced parameters which are attributed to the development of localized moments at the Ce ions as the Y concentration increases.
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Luengo, C. A., J. G. Huber, J. G. Sereni, A. R. Sweedler, J. M. Cotignola, and M. B. Maple. "Low temperature specific heat of ThU." Solid State Communications 10, no. 5 (1972): 459.
Abstract: The low temperature specific heat of the weakly magnetic system Image U has been measured in both the normal and superconducting states. U impurities are found to enhanve the normal state electronic specific heat coefficient γ at an unusually large rate of 4.85 ± 0.50 mJ/mole °K2 at. % U. The specific heat jump at the superconducting transition for an alloy of composition 0.075 at. % U follows the BCS law of corresponding states suggesting that the system Image U is essentially non-magnetic at superconducting temperatures.
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Núñez Regueiro, M., M. A. Izbizky, and P. Esquinazi. "Thermal conductivity and “disorder” in high temperature superconductors." Solid State Communications 67, no. 4 (1988): 401–404.
Abstract: We analyze the controversial thermal conductivity results on high temperature superconductors by scaling the data with material parameters to compare them to other materials with similar behaviour. We show that they have the same general features observed in amorphous and disordered crystalline materials. Possible origins of the disorder are discussed.
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