Fabrication of microstructured devices of the unconventional superconductor CeCoIn5 for investigations of isolated grain boundaries

Grain boundaries are critical for determining the functionality of polycrystalline materials. Here we present on the structural $&$ transport properties of grain boundaries in the unconventional superconductor CeCoIn$_5$. We provide a detailed recipe for the fabrication of isolated grain boundary devices from of as-grown polycrystalline samples of CeCoIn$_5$. Electron backscattered diffraction imaging of polycrystalline CeCoIn$_5$ samples reveals an abundance of $90^\circ$ misorientation grain boundaries suggesting a preferential nucleation of CeCoIn$_5$ grains with 90$^\circ$ misorientation over a random distribution of grain orientations. Transport measurements across grain boundary devices establish coherence of superconductivity and allows us to establish a lower bound on the critical current density for the grain boundaries. Our work opens new possibilities for fabrication of quantum devices such as Josephson-junctions out of bulk unconventional superconducting materials.

💡 Research Summary

The paper presents a comprehensive study of grain boundaries (GBs) in the unconventional heavy‑fermion superconductor CeCoIn₅ and demonstrates a practical route to fabricate isolated GB devices for transport measurements. Polycrystalline CeCoIn₅ ingots were synthesized by high‑temperature melting, rapid quenching, and a prolonged anneal at 600 °C. The resulting bulk material was mechanically thinned to plates of 10–20 µm thickness and polished to a surface roughness of ~40 nm, enabling high‑quality electron backscatter diffraction (EBSD) imaging. EBSD, combined with energy‑dispersive X‑ray spectroscopy (EDS), identified three phases: the target CeCoIn₅ (≈60–70 % volume), cubic CeIn₃, and tetragonal Ce₂CoIn₈. Grain sizes ranged from 5 to 100 µm, and a striking statistical prevalence of 90° misorientation grain boundaries was observed—about 40 % of all boundaries were rotated by 90° about the