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We investigate the reversible magnetization in the mixed state of a batch of Bi2.12Sr1.90Ca1.02Cu1.96O8 + δ(Bi-2212) ceramics with different oxygen concentrations δ and superconducting transition temperatures Tcbetween 50 and 92 K. Additional data for a single crystal (Tc= 85 K) demonstrate the validity of the effective-mass model with essentially infinite anisotropy.

Abstract: In order to document the behavior of the mean-field mixed-state specific heat of an isotropic. strongly type-II superconductor (i.e., with a large value of the Ginzburg parameterk), and to provide a basis for comparison with high-temperature superconductors, we measured the specific heatC of the alloy Nb0.77Zr0.23 withT c = 10.8K, B c2 (0) = 7.9T, in magnetic fieldsB = 0, 0.2, 1.0, 12, 2.0, 2.4. 3.0, 3.3. 4.0. 4.4, 4.8, 5.2, 6.0. 6.6, 7.2 and 10 T. The values of the upper critical fieldB c2 ( T), thermodynamic critical fieldB c (T), Ginzburg parameterk(T), and coefficient γ(B) = limT0(C(T. B)/T) are derived from the specific heat data and found to be in agreement with the GLAG theory in the dirty limit. The behavior of the mixed-state specific heat is analyzed in terms ofC el /T,∂(C el /T)/∂B, and∂(C el /T)/∂T vs. Tcurves, whereC el is the electronic contribution to the specific heat.

We report on the absence of the so-called fishtail or peak effect in the magnetisation curves of properly oxygenated high purity (5N) single crystals of YBa2Cu3O7-d. As we recently reported [1] high pressure oxygenation procedures are suitable to produce a monotonous dependence of the critical current density with the magnetic field. In this article we report furthermore how to reversibly produce or remove this effect on the same crystal by proper oxygenation methods. Along with the high purity of the samples, — due to crystal growth in non reactive BaZrO3 crucibles —, this proves that at least in pure samples the fishtail effect is due to different oxygenation states and/or oxygen distributions. In less pure samples, however, other sources for this anomaly like metallic impurities can act as an additional source for the fishtail anomaly.

We present local probe tunneling spectroscopy of Bi2Sr2CaCu2O8+d single crystals for different oxygen concentrations, from optimally doped (Tc=92.2 K) to highly overdoped (Tc=56.0 K) phases. With increasing oxygen overdoping, the superconducting gap (?p) is reduced and the dip structure beyond ?p at negative sample bias1 shifts toward the Fermi energy. Apart from the shift in energy of these features, the generic shape of the tunneling spectra remains unchanged. The gap roughly scales with Tc, and 2?p/kBTc stays large even in the highly overdoped phase. We also present preliminary results on the temperature dependence of the tunneling spectra. They are consistent with a gap that is largely independent on temperature up to the vicinity of Tc

In order to document the behavior of the mean-field mixed-state specific heat of an isotropic. strongly type-II superconductor (i.e., with a large value of the Ginzburg parameterk), and to provide a basis for comparison with high-temperature superconductors, we measured the specific heatCof the alloy Nb0.77Zr0.23withTc= 10.8K, Bc2(0) = 7.9T, in magnetic fieldsB= 0, 0.2, 1.0, 12, 2.0, 2.4. 3.0, 3.3. 4.0. 4.4, 4.8, 5.2, 6.0. 6.6, 7.2 and 10 T. The values of the upper critical fieldBc2( T), thermodynamic critical fieldBc(T), Ginzburg parameterk(T), and coefficient γ(B) = limT0(C(T. B)/T)are derived from the specific heat data and found to be in agreement with the GLAG theory in the dirty limit. The behavior of the mixed-state specific heat is analyzed in terms ofCel/T,∂(Cel/T)/∂B,and∂(Cel/T)/∂Tvs. Tcurves, whereCelis the electronic contribution to the specific heat.

We report on the first HTS crystal growth in BaZrO3crucibles under very high gas pressure. YBa2Cu4O8(Y124) crystals were grown in an autoclave under 1400 bar of pure oxygen. The eutectic temperature was determined to be 1113°C. X-ray analysis and electronic (EDX) micrographs showed that the crystals were contamination-free. The high (Tc=81.5K) and sharp superconducting transition and the small magnetic hysteresis further established the purity of these Y124 crystals. In particular, no “fishtail” anomaly, but a monotonous decrease of the hysteresis was observed in magnetic fields up to 5.5T and down to 10K. The use of BaZrO3crucibles shows that this stoechiometric and untwinned compound exhibits an intrinsically low pinning.

This paper presents the new 2D electrostatic particle-in-cell code FENNECS developed to study the formation of magnetized non-neutral plasmas in geometries with azimuthal symmetry. This code has been developed in the domain of gyrotron electron gun design, but solves general equations and can be applied in other domains of plasma physics. FENNECS is capable of simulating electron-neutral collisions using a Monte Carlo approach and considers both elastic and inelastic (ionization) processes. It is also capable of solving the Poisson equation on domains with arbitrary geometries with either Dirichlet or natural boundary conditions. The Poisson solver is based on a meshless Finite Element Method, called web-splines, based on b-splines of any order, and used for the first time in the domain of plasma physics. In addition, the effect of fast ions colliding with the electrodes and causing ion induced electron emission at the electrode surfaces has been implemented in the code. In this paper, the governing equations solved by FENNECS and the numerical methods used to solve them are presented. A number of verification cases are then reported. Finally, the parallelization scheme used in FENNECS and its parallel scalability are presented. [ABSTRACT FROM AUTHOR]