Abstract Body

For technological applications, there are intense efforts to boost the critical current density J_c to reach metrics requisite for numerous applications, e.g., magnets for fusion reactors, proton irradiation therapy, motors for aircraft. The ultimate upper limit for J_c is the depairing current density J_d — the current that imparts sufficient kinetic energy to break apart electron pairs constituting the supercurrent. However, the motion of vortices, magnetic flux lines that penetrate type-II superconductors, introduces dissipation that restricts J_c. Consequently, the typical approach to enhancing J_c is to add defects to immobilize (pin) the vortices. Yet, when optimized, this method is only capable of achieving a maximum J_c of ~30% J_d, though most studies struggle to achieve even a small fraction of this ceiling. Recently, we combined raising the J_d (ceiling) itself by a thermodynamic route with our previously developed methods of tailoring the size and density of pinning centers in REBa₂Cu₃O_y coated conductors (CCs). We obtained J_c∼150 MA/cm² at 4.2 K in self-field [2]. Moreover, we demonstrated a similar enhancement in the depairing current in three classes of iron-based superconductors (1111-type, 11-type, 122-type) [3]. Our combination approach also allows us to slow the rate of thermally activated vortex motion (creep) in several superconducting material systems by reducing the Ginzburg number, a parameter that correlates with vortex creep rates. The resulting high J_c, slow creep rate, and low anisotropy constitute a serious step towards making superconductors using this combined approach attractive for applications. Detailed microstructural and superconducting properties will be presented.

References

[1] M. Miura et al., NPG Asia Materials 9(2017) e447.
[2] M. Miura et al., NPG Asia Materials 14(2022) 85.
[3] M. Miura et al., Nature Materials (Published: 18 July 2024, DOI: https://doi.org/10.1038/s41563-024-01952-7).

Acknowledgment

The work at Seikei University was supported by JST-FOREST (Grant Number JPMJFR202G). A part of this work was supported by JSPS KAKENHI (23H01453 and 23KK0073).