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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Seyfarth, G., D. Jaccard, P. Pedrazzini, A. Krzton-Maziopa, E. Pomjakushina, K. Conder, and Z. Shermadini. "Pressure cycle of superconducting Cs0.8Fe2Se2 : A transport study." Solid State Communications 151, no. 10 (2011): 747–750.
Abstract: We report measurements of the temperature and pressure dependence of the electrical resistivity (Ï) of single-crystalline iron-based chalcogenide Cs0.8Fe2Se2. In this material, superconductivity with a transition temperature Tc~30K source develops from a normal state with extremely large resistivity. At ambient pressure, a large “hump†in the resistivity is observed around 200 K. Under pressure, the resistivity decreases by two orders of magnitude, concomitant with a sudden Tc suppression around pc~30K. Even at 9 GPa a metallic resistivity state is not recovered, and the Ï(T) “hump†is still detected. A comparison of the data measured upon increasing and decreasing the external pressure leads us to suggest that the superconductivity is not related to this hump.
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Giriat, G., Z. Ren, P. Pedrazzini, and D. Jaccard. "High pressure investigation of superconducting signatures in CeCu2Si2: ac-magnetic susceptibility, ac-heat capacity, resistivity and thermopower." Solid State Communications 209–210 (2015): 55–58.
Abstract: Taking advantage of a novel multiprobe setup we have measured, on a unique sample, the ac-magnetic susceptibility, the resistivity, the ac-specific heat and the thermopower of the superconductor heavy fermion CeCu2Si2 under pressure up to 5.1 GPa. At the superconducting transition temperature Tc, the Meissner signal corresponds to that expected for the sample volume and coincides with the specific heat jump and the resistive transition completion temperatures. Differing from previous observations, here the susceptibility measurements did not reveal any anomaly in the vicinity of the resistive transition onset.
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Kim, J., N. Haberkorn, K. Gofryk, M. J. Graf, F. Ronning, A. S. Sefat, R. Movshovich, and L. Civale. "Superconducting properties in heavily overdoped Ba(Fe0.86Co0.14)2As2 single crystals." Solid State Communications 201 (2015): 20–24.
Abstract: Abstract
We report the intrinsic superconducting parameters in a heavily overdoped Ba(Fe1−xCox)2As2 (x=0.14) single crystal and their influence in the resulting vortex dynamics. We find a bulk superconducting critical temperature of 9.8 K, magnetic penetration depth λab (0)=660±50 nm, coherence length ξab (0)=6.4±0.2 nm, and the upper critical field anisotropy γT→Tc≈3.7. The vortex phase diagram, in comparison with the optimally doped compound, presents a narrow collective creep regime. The intrinsic pinning energy plays an important role in the resulting vortex dynamics as compared with similar pinning landscape and comparable intrinsic thermal fluctuations.
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Kim, J., N. Haberkorn, E. Nazaretski, R. de Paula, T. Tan, X. X. Xi, T. Tajima, R. Movshovich, and L. Civale. "Strong magnetic field dependence of critical current densities and vortex activation energies in an anisotropic clean MgB2 thin film." Solid State Communications 204 (2015): 56–60.
Abstract: We report the influence of two-band superconductivity on the flux creep and the critical current densities of a MgB2 thin film. The small magnetic penetration depth of λ=50±10 nm at T=4 K is related to a clean π-band. We find a high self-field critical current density Jc, which is strongly reduced with applied magnetic field, and attribute this to suppression of the superconductivity in the π-band. The temperature dependence of the creep rate S (T) at low magnetic field can be explained by a simple Anderson–Kim mechanism. The system shows high pinning energies at low field that are strongly suppressed by high field.
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Haberkorn, N., S. Suárez, S. L. Bud'ko, and P. C. Canfield. "Strong pinning and slow flux creep relaxation in Co-doped CaFe2As2 single crystals." Solid State Communications 318 (2020): 113963.
Abstract: We report on measurements of critical current densities Jc and flux creep rates S of freestanding Ca(Fe1−xCox)2As2 (x ≈ 0.033) single crystals with Tc ≈ 15.7 K by performing magnetization measurements. The magnetic field dependences of Jc at low temperature display features related to strong pinning. In addition, we find that the system displays small flux creep rates. The characteristic glassy exponent, μ, and the pinning energy, U0, display exceptional high values for pristine crystals. We find that for magnetic fields between 0.3 T and 1 T, μ decreases from ≈ 2.8 to ≈ 2 and U0 remains ≈ 300 K. Analysis of the pinning force indicates that the mechanism is similar to the observed in polycrystalline systems in which grain boundaries and random disorder produce the vortex pinning. Considering the large U0 observed in the single crystal, we attempt to improve the pinning by adding random point disorder by 3 MeV proton irradiation with a fluence of 2 × 1016 proton/cm2. The results show that, unlike other iron-based superconductors, the superconducting fraction is sharply reduced by irradiation. This fact indicates that the superconductivity in the system is extremely fragile to an increment in the disorder. The superconducting volume fraction in the irradiated crystal systematically recovers after removal disorder by thermal annealing, which evidences as to the observation of critical state in curves of magnetization versus magnetic field. No features related to a reentrant antiferromagnetic transition are observed for the irradiated sample.
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