Low-frequency flux noise in current-carrying high critical temperature superconducting films

We demonstrate that 3.5-MeV oxygen irradiation can markedly enhance the in-field critical current of commercial 2 nd generation superconducting tapes with an exposure time of just one second per 0.8 cm 2 . The speed demonstrated here is now at the level required for an industrial reel-to-reel post-processing. The irradiation is made on production line samples through the protective silver coating and does not require any modification of the growth process. From TEM imaging, we identify small clusters as the main source of increased vortex pinning. 2Increasing the current carrying capacity of 2 nd generation (2G) YBCO high temperature superconducting (HTS) wires in the presence of high magnetic fields is critical for the commercialization of HTS based rotating machine applications such as lightweight and compact off-shore wind turbines and motors as well as various HTS magnet applications [1][2][3][4]. For these, operation in magnetic fields of several Tesla and at temperatures around 30K is envisioned. Although conductors of hundreds of meters in length with self-field critical current densities J c of more than 3 -4 MA/cm 2 (more than 300 -400 A/cm-width) at 77 K can now reliably be manufactured, the rapid suppression of J c in even modest applied magnetic fields continues to be a major challenge for HTS conductor development.In recent years, impressive advances in the in-field performance of short-length samples have been achieved [5][6][7][8][9][10], largely due to the strict control over the micro-and nanostructures. The formation of the desired pinning centers depends sensitively on the film deposition technique and substrate architecture. For instance, self-assembled nanorods can be engineered in films grown by pulsed laser deposition (PLD) or MOCVD from material containing excess metal oxides such as BaZrO 3 [11][12][13][14], BaSnO 3 [15] or BaHfO 3 [16], whereas the deposition of films with excess Zr using metal organic deposition (MOD) on single-crystal substrates [17] and on IBAD substrates [18] does not yield nanorods but nanoparticles. In general, the enhanced vortex pinning arises from the complex combined effects of the introduced second phases (nanorods or nanoparticles), additional structural disorder such as twin boundaries, stacking faults and point defects, as well as from isotropic pinning due to strain fields [5,17]. In short-length samples, critical current densities as high as ~ 7 MA/cm 2 at 30 K and 9 T applied parallel to caxis have been reported [9]. The translation of these advances into a reliable large-scale production process is a time consuming process currently under development.An alternative to increase the critical current density by modifying the chemical synthesis is afforded by particle irradiation, which may be applicable to all superconducting materials. Depending on the mass and energy of the ions and the properties of the superconducting material, irradiation enables the creation of defects with well-controlled density and topology, such as points, clusters or tracks. The...

We present resistivity and magnetization measurements on proton-irradiated crystals demonstrating that the superconducting state in the doped topological superconductor NbxBi2Se3 (x = 0.25) is surprisingly robust against disorder-induced electron scattering. The superconducting transition temperature Tc decreases without indication of saturation with increasing defect concentration, and the corresponding scattering rates far surpass expectations based on conventional theory. The lowtemperature variation of the London penetration depth ∆λ(T ) follows a power law (∆λ(T ) ∼ T 2 ) indicating the presence of symmetry-protected point nodes. Our results are consistent with the proposed robust nematic Eu pairing state in this material.

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Mixed pinning landscapes in superconductors are emerging as an effective strategy to achieve high critical currents in high, applied magnetic fields. Here, we use heavy-ion and proton irradiation to create correlated and point defects to explore the vortex pinning behavior of each and combined constituent defects in the iron-based superconductor Ba0.6K0.4Fe2As2 and find that the pinning mechanisms are non-additive. The major effect of p-irradiation in mixed pinning landscapes is the generation of field-independent critical currents in very high fields. At 7 T ‖ c and 5 K, the critical current density exceeds 5 MA/cm2.

YBa2Cu3O7-δ coated conductors (CCs) have achieved high critical current densities (Jc) that can be further increased through the introduction of additional defects using particle irradiation. However, these gains are accompanied by increases in the flux creep rate, a manifestation of competition between the different types of defects. Here, we study this competition to better understand how to design pinning landscapes that simultaneously increase Jc and reduce creep. CCs grown by metal organic deposition show non--monotonic changes in the temperature--dependent creep rate, S(T). Notably, in low fields, there is a conspicuous dip to low S as the temperature (T) increases from 20 K to 65 K. Oxygen--, proton--, and Au--irradiation substantially increase S in this temperature range. Focusing on an oxygen--irradiated CC, we investigate the contribution of different types of irradiation-induced defects to the flux creep rate. Specifically, we study S(T) as we tune the relative density of point defects to larger defects by annealing both an as--grown and an irradiated CC in O2 at temperatures TA = 250°C to 600°C. We observe a steady decrease in S(T > 20 K) with increasing TA, unveiling the role of pre--existing nanoparticle precipitates in creating the dip in S(T) and point defects and clusters in increasing S at intermediate temperatures.

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We demonstrate a 2-fold increase of the in-field critical current of AMSC's standard 2G coil wire by irradiation with 18 MeV Au ions. The optimum pinning enhancement is achieved with a dose of 6x10 11 Au ions/cm 2 . Although the 77 K, self-field critical current is reduced by about 35%, the in-field critical current (H//c) shows a significant enhancement between 4 -50K in fields >1 T. The process was used for the roll-to-roll irradiation of AMSC's standard 46 mm wide production coated conductor strips which were further processed in to standard copper laminated coil wire. The long length wires show the same enhancement as attained with short static irradiated samples. The roll-to-roll irradiation process can be incorporated in the standard 2G wire manufacturing with no modifications to the current process. The enhanced performance of the wire will benefit rotating machine and magnet applications.