Designing high-performance superconductors with nanoparticle inclusions: comparisons to strong pinning theory

Sarah C. Jones; Masashi Miura; Ryuji Yoshida; Takeharu Kato; Leonardo Civale; Roland Willa; Serena Eley

doi:10.1063/5.0057479

paper

Designing high-performance superconductors with nanoparticle inclusions: comparisons to strong pinning theory

arXiv:2105.10204 · doi:10.1063/5.0057479

Abstract

One of the most promising routes for achieving unprecedentedly high critical currents in superconductors is to incorporate dispersed, non-superconducting nanoparticles to control the dissipative motion of vortices. However, these inclusions reduce the overall superconducting volume and can strain the interlaying superconducting matrix, which can detrimentally reduce $T_{c}$ . Consequently, an optimal balance must be achieved between the nanoparticle density $n_{p}$ and size $d$ . Determining this balance requires garnering a better understanding of vortex-nanoparticle interactions, described by strong pinning theory. Here, we map the dependence of the critical current on nanoparticle size and density in (Y $_{0.77}$ ,Gd $_{0.23}$ )Ba $_{2}$ Cu $_{3}$ O $_{7 - δ}$ films in magnetic fields up to 35 T, and compare the trends to recent results from time-dependent Ginzburg-Landau simulations. We identify consistencies between the field-dependent critical current $J_{c} (B)$ and expectations from strong pinning theory. Specifically, we find that that $J_{c} \propto B^{- α}$ , where $α$ decreases from $0.66$ to $0.2$ with increasing density of nanoparticles and increases roughly linearly with nanoparticle size $d / ξ$ (normalized to the coherence length). At high fields, the critical current decays faster ( $\sim B^{- 1}$ ), suggestive that each nanoparticle has captured a vortex. When nanoparticles capture more than one vortex, a small, high-field peak is expected in $J_{c} (B)$ . Due to a spread in defect sizes, this novel peak effect remains unresolved here. Lastly, we reveal that the dependence of the vortex creep rate $S$ on nanoparticle size and density roughly mirrors that of $α$ , and compare our results to low- $T$ nonlinearities in $S (T)$ that are predicted by strong pinning theory.

Designing high-performance superconductors with nanoparticle inclusions: comparisons to strong pinning theory

Abstract

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