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Haberkorn, N., and V. F. Correa. "Effect of low-temperature thermal annealing on the vortex dynamics of metastable β-Bi2Pd single crystals." Physica C: Superconductivity and its Applications 598 (2022): 1354051.
Abstract: We study the vortex dynamics on β-Bi2Pd single crystals with a superconducting critical temperature of 5.1 K. The upper critical fields and magnetic penetration depth are determined from magnetization measurements. At low temperatures, the self-field critical current density (Jc) is ≈ 20 kA/cm2. The vortex pinning energy, extracted from an Anderson-Kim approximation, is between 340 K and 140 K for fields between 100 G and 600 G. Differential scanning calorimetric measurements show that the crystals start to transform into the alpha-phase at temperatures as low as 60 °C. Short annealing at 100 °C modifies the pinning landscape increasing Jc mainly at temperatures below 3 K. The angular dependence of Jc from electrical transport experiments shows a broad peak when the magnetic field is parallel to the crystallographic c-axis, indicating the presence of correlated disorder.
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Puig, J., N. R. Cejas Bolecek, J. Aragón Sánchez, M. I. Dolz, M. Konczykowski, and Y. Fasano. "Bridge in micron-sized Bi2Sr2CaCu2O8 sample act as converging lens for vortices." Physica C: Superconductivity and its Applications 590 (2021): 1353948.
Abstract: We report on direct imaging of vortex matter nucleated in micron-sized BiSrCaCuO superconducting samples that incidentally present a bridge structure. We find that when nucleating vortices in a field-cooling condition the deck of the bridge acts as a converging lens for vortices. By means of Bitter decoration images allowing us to quantify the enhancement of vortex-vortex interaction energy per unit length in the deck of the bridge, we are able to estimate that the deck is thinner than m. We show that the structural properties of vortex matter nucleated in micron-sized thin samples are not significantly affected by sample-thickness variations of the order of half a micron, an important information for type-II superconductors-based mesoscopic technological devices.
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van Dalen, A. J. J., R. Griessen, S. Libbrecht, E. Osquiguil, and Y. Bruynseraede. "Observation of quantum creep in oxygen deficient YBa2Cu3O7-? at fields up to 7 T." Physica C: Superconductivity and its applications 235-240, no. PART 5 (1994): 2959–2960.
Abstract: Superconducting current densities js and dynamic relaxation rates Q ? d ln js/d ln (dBe/dt) in an oxygen deficient YBa2Cu3O7-? epitaxial film were measured as a function of temperature (1.5K < T < Tirr) in magnetic fields up to 7 T by means of high sensitivity capacitance torquemeters. Below 5 K, the relaxation rate remains high and does not extrapolate to Q = 0 at T = 0K. This is associated to the quantum tunneling of vortices through the energy barrier separating two adjacent vortex configurations. In the case of ohmic dissipation the quantum creep rate is proportional to the normal state resistivity ?{variant}n(0) at T = 0 K. In order to check this theoretical prediction we measured Q as a function of the oxygen content of the sample. The quantum creep rate increases systematically with increasing ?{variant}n(0). However, Q remains finite even when ?{variant}n = 0.
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Libbrecht, S., A. J. J. van Dalen, B. Wuyts, M. Maenhoudt, Z. X. Gao, E. Osquiguil, R. Griessen, and Y. Bruynseraede. "Magnetic properties of oxygen deficient Yba2Cu3Ox thin films." Physica C: Superconductivity and its applications 235-240, no. PART 5 (1994): 2889–2890.
Abstract: We have invesitgated several superconducting properties of oxygen defiecient YBa2Cu3Ox thin films, with oxygen contents ranging from x = 6.55 to x = 7. By means of torque magnetometry, the temperature dependence of the superconducting current dendity js and relaxation rate of the magnetization Q is measured in an (almost perpendicular) applied magnetic induction of 0.6 T. As the oxygen content is reduced, js decreases, whereas Q increases. Both properties are influenced by the decreased dpoing level as well as the enhanced anisotropy of oxygen depleted YBa2Cu3Ox. Using the Generalixed Inversion Scheme derived by Schnak et al. we obtain the current dependence of the activation energy U(f). We show that U(j) is lowered when the oxygen content is reduced.
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Dhalle, M., W. Boon, E. Osquiguil, C. Van Haesendonck, Y. Bruynseraede, J. Kwarciak, and O. Van Der Biest. "Correlation between critical current and resistivity in YBa2Cu3O7." Physica C: Superconductivity and its applications 185-189, no. PART 4 (1991): 2447–2448.
Abstract: Critical current versus temperature measurements were carried out in ceramic YBa2Cu3O7 samples. The samples were all prepared using the same sintering procedure, but starting from powders obtained by different wet and dry methods. All samples showed a linear Jc vs. T behaviour, typical of Josephson weak-link coupling, with a slope that depends on the preparation method. Using the Ambegaokar-Baratoff relation for Jc, the difference in slopes can be attributed to a change in the characteristic value of the junction resistance. This value turns out to be clearly correlated with the resistivity in the normal state.
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Neerinck, D., K. Temst, M. Baert, E. Osquiguil, C. Van Haesendonck, Y. Bruynseraede, A. Gilabert, and I. K. Schuller. "Thermally induced transition in the vortex lattice of Ge/Pb multilayers." Physica C: Superconductivity and its applications 185-189, no. PART 3 (1991): 2061–2062.
Abstract: We report on a novel magnetic field dependence of the critical current density of M.B.E. grown Ge/Pb insulator/superconductor multilayers. When the magnetic field is applied perpendicular to the layers, the critical current density Jc drops to a minimum, followed by a broad maximum before finally decaying monotonously to zezero with increasing magnetic field. The dependence of this effect on pinning strength, temperature, and layer thickness suggests either a thermally driven coupling/decoupling transition, or melting of the vortex lattice.
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Martin, J. I., B. Wuyts, M. Maenhoudt, E. Osquiguil, J. L. Vicent, V. V. Moshchalkov, and Y. Bruynseraede. "Sign reversal of the flux flow Hall effect in oxygen deficient YBa2Cu3Ox films." Physica C: Superconductivity and its applications 235-240, no. PART 2 (1994): 1451–1452.
Abstract: The Hall effect of high temperature superconductors has been reported to slow in some cases a striking sign reversal near Tc, the origin of which is not yet fully understood. We report on measurements of the Hall effect in the mixed state of oxygen deficient YBa2Cu3Ox thin films, for 7?
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El Azrak, A., L. A. de Vaulchier, N. Bontemps, C. Thivet, M. Guilloux-Viry, A. Perrin, B. Wuyts, and E. Osquiguil. "Optical and transport measurements of YBa2Cu3O6+x thin films (0.38?x?1)." Physica C: Superconductivity and its applications 235-240, no. PART 2 (1994): 1431–1432.
Abstract: We report optical reflectivity and transmission measurements at room temperature on a set of five YBa2Cu3O6+x films for 0.38?x?, and ?{variant}(T) resistivity data down to 10K, prepared from a single YBa2Cu3O7 thin film. In contrast with x=1, as x decreases, the scattering rate deduced from the optical conductivity departs from its linear variation with ?, in correlation with the absence of linearity of ?{variant}(T) versus temperature.
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Wuyts, B., M. Maenhoudt, S. Libbrecht, Z. X. Gao, E. Osquiguil, V. V. Moshchalkov, and Y. Bruynseraede. "Linear relation between the Hall angle slope and the carrier density in YBa2Cu3Ox films." Physica C: Superconductivity and its applications 235-240, no. PART 2 (1994): 1369–1370.
Abstract: A universal relation cot?H??{variant}/RHB = ?T2 + C for the Hall angle ?H has been experimentally observed served in a wide variety of high-Tc systems. In contrast to the linear temperature dependence of the resistivity ?{variant} or the inverse Hall coefficient R-1H, the T2-dependence of cot?H remains valid in under- and overdoped systems. We present a systematic study of cot?H(T) in oxygen deficient epitaxial YBa2Cu3Ox thin films. We find evidence for a linear relation between ?, the slope of cot?H versus T2, and the carrier concentration. Moreover, we find a steep increase in the intercept C = cot?H (T = 0) below x ? 6.6.
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Núñez Regueiro, M., P. Esquinazi, M. A. Izbizky, C. Duran, D. Castello, J. Luzuriaga, and G. Nieva. "Evidence of tunneling systems through thermal and acoustic measurements in ceramic materials." Physica C: Superconductivity and its applications 153-155, no. PART 2 (1988): 1016–1017.
Abstract: We have neasured the sound velocity, internal friction, thermal conductivity and specific heat of La-based and (Y/Eu)- based ceramics. The low temperature data can be understood in terms of the Tunneling Model assuming the existence of Tunneling Systems (TS). From these measured properties we obtain values for the parameter C=P?2/?v2, where P is the density of states of TS, ? the coupling constant between phonons and TS, ? the mass density and v the sound velocity close to those obtained for amorphous and “orientational” disordered crystalline materials. Our data would indicate that the TS are intrinsic defects independent of the sample porosity.
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