The cause of ‘weak-link’ grain boundary behaviour in polycrystalline Bi₂Sr₂CaCu₂O₈and Bi₂Sr₂Ca₂Cu₃O₁₀superconductors

Abstract

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Study of anisotropy in the superconducting properties of FeTe0.55Se0.45 single crystal grown by the self-flux method

“…These asymmetric transition widths for H∥c and H∥ab, suggest the existence of anisotropy in the current single crystal. Similar field broadening of resistivity with the magnetic field have been observed in cuprates and other IBSs [40,42,43]. Moreover, the superconducting transition width for the H∥c is broader than H∥ab, suggesting the vortex motion is anisotropic.…”

The Conundrum of Strongly Coupled Supercurrent Flow in Both Under- and Over-doped Bi-2212 Round Wires

“…Moreover, the Bi-2212 wires lack the hysteretic field-increasing, field-decreasing, weak-link signature displayed by Bi-2223 [10]. Indeed a recent study found evidence of well-connected grains in an untextured bulk Bi-2212 sample but not in a similarly prepared Bi-2223 bulk sample [18]. This paradox of greatly divergent connectivity between two very similar siblings is what has stimulated the present study.…”

“…We know that round wire Bi-2212 shows great promise for ultra high field solenoids [2,19], for plasma fusion use [20] and for accelerator dipoles [12]. All such applications are made more attractive by higher J c values and because we conclude that the J c of the best present Bi-2212 [13,14] is still less than 1% of Bi-2212's depairing current density [18,21], it seems clear that the active superconducting cross section is significantly less than unity. Understanding where obstacles to current flow occur and what they are is key to further enhancing the J c .…”

Weak emergence in the angular dependence of the critical current density of the high temperature superconductor coated conductor REBCO

“…At J c , fluxons flow along grain boundary channels with the fluxons in the grains strongly pinned and stationary [80]. Given that the current density in high fields for most polycrystalline materials is typically less than just a few percent of the depairing current density [110,111], one can consider them as granular to a good approximation. The grain boundaries are complex structures but it is reasonable to assume that they act as barriers that include a central region of low T c and/or higher resistivity where the superconducting order parameter and the (transport) current density that can cross the grain boundary are severely depressed [112].…”