Toward superconducting critical current by design

Abstract: We present the new paradigm of critical current by design. Analogous to materials by design, it aims at predicting the optimal defect landscape in a superconductor for targeted applications by elucidating the vortex dynamics responsible for the bulk critical current. To highlight this approach, we demonstrate the synergistic combination of critical current measurements on commercial high-temperature superconductors containing self-assembled and irradiation tailored correlated defects by using large-scale time-dependent Ginzburg-Landau simulations for vortex dynamics.

• The paper demonstrates a new paradigm using TDGL simulations to optimize defect arrangements that enhance the critical currents in high-temperature superconductors.
• It employs 3D numerical modeling on REBCO conductors with nanorods and irradiation-induced defects, revealing non-additive vortex pinning effects.
• The findings provide a strategic framework for engineering next-generation superconductors through precise control of defect concentrations and orientations.

Critical Current by Design in Superconductors

The research presented in "Toward superconducting critical current by design" delineates a new paradigm aimed at optimizing superconducting materials' critical currents through intentional design of defect landscapes. By leveraging the time-dependent Ginzburg-Landau (TDGL) simulations, this study explores the vortex dynamics that impede or facilitate the maximal critical current in high-temperature superconductors. The authors' approach allows for predicting the optimal arrangement and concentration of defects to tailor the critical current for specific applications.

Key Insights and Methodology

The study hinges on the critical current by design paradigm, an offshoot of the materials by design concept, which utilizes computational simulations to dictate the interplay between superconducting vortices and material defects. In superconductors, vortices, which are non-superconducting core regions surrounded by superconducting currents, move under the influence of magnetic fields, causing a deterioration in superconductivity known as dissipation. Defects within the material can serve as pinning centers that immobilize these vortices, enhancing the critical current that characterizes the peak dissipation-free current the material can sustain.

Explicitly, the paper covers:

1. Defect Interaction and Pinning: The intricate interaction between defects and vortices directly affects the critical current. The study accounts for non-additive effects where defects can synergistically enhance or diminish the critical current.
2. Numerical Simulations: The TDGL framework serves as the computational foundation for understanding these vortex-defect interactions. Simulations are conducted in a three-dimensional domain to capture realistic interactions for type-II superconductors. The solver employed is optimized for high-performance computing on GPUs, allowing for large-scale modelling.
3. Experimental Validation: The simulations are benchmarked against experimental findings on REBCO coated conductors with self-assembled BZO nanorods either included or absent and subjected to splayed heavy-ion irradiation. The combination of nanorods and irradiation introduces correlated defect landscapes which are investigated.

Numerical and Experimental Results

Experimental and numerical analyses of samples with self-assembled barium zirconate (BZO) nanorods and irradiation-induced columnar defects reveal non-trivial interactions among different types of pinning landscapes. For instance, introducing irradiation tracks at a 45-degree angle to the c-axis in REBCO conductors initially containing nanorods led to a critical current peak shift, illustrating the powerful non-additive effects of defect orientations.

• Defect Concentration Optimization: The simulation results provide critical insights for determining optimal defect concentrations. With increased nanorod concentration, the critical current initially rises until reaching a saturation point beyond which further increases have negligible effects.
• Dual-Irradiation Strategy: Employing splayed defects from irradiation at symmetric angles relative to the c-axis flattens the angular dependence of critical current, promoting isotropic enhancements.

Implications and Future Directions

This research widens the scope for designing superconductors with enhanced critical currents by constructing optimal defect landscapes through computational insights. As computational capabilities continue to expand, the practicality of predicting critical currents based on superconductor microstructures nears realization. This could substantially benefit applications that rely on high-performing superconductors, such as advanced magnet technologies, power grids, and transportation systems.

The findings underscore the necessity for further refinement of simulation techniques, particularly in incorporating realistic thermal noise and more complex defect morphologies. Future research could explore the dynamics at higher temperatures, closer to operational ranges, and investigate more complex pinning environments.

In sum, this paper advances the understanding of superconducting critical currents and provides a strategic foundation for engineering next-generation superconducting materials through defect design, validated by both theoretical simulations and empirical evidence.