Condensed-Matter Physics & Materials Science Seminar

Since the discovery of superconductivity in iron-based superconductors, great efforts have been devoted to the preparation of films and wires for practical applications. Among these iron-based superconductors FeSe has several practical advantages over pnictides. FeSe has the simplest structure and less toxicity compared to the other As-based compounds. They also possess a high upper critical field Hc2 and extremely low Hc2 anisotropy. Furthermore, FeSe with Tczero ~8 K and Tconset ~10 K shows that the application of pressure leads to a significant enhancement of Tc up to 37 K under high pressure. These aspects make FeSe to be a more promising material for applications in high Jc superconducting wires. We succeeded in fabricating mono- and multi-core wires of FeSe using the Fe-diffusion powder-in-tube (PIT) method. The seven-core superconducting wires showed a transport Jc as high as 1027 A/cm2.1 What is more interesting is that the transition temperature Tczero was observed at 10.5 K, which is about 2 K higher than that of the bulk.1,2 These results indicate that the Fe-diffusion PIT method is highly suitable for fabricating FeSe superconducting wires.
Recently, a KxFe2-ySe2 superconductor with Tc 30 K was discovered. KxFe2-ySe2 could be a potential material for practical applications under high magnetic fields because of the high Hc2 and small anisotropy. However, the procedure for producing KxFe2-ySe2 single crystals is complicated and time-consuming. The simplification of the synthesis is crucial to fabricate superconducting wires. We have established a simple process that allows for the one-step synthesis of KxFe2-ySe2 single crystals, which exhibit high critical current density Jc.3 We will also report the details of the synthesis, transport properties and microstructures of the samples.

[1] T. Ozaki, et al, arXiv: 1103.3602, J. Appl. Phys (to be published)
[2] T. Ozaki, et al, J. Appl. Phys. 111, 013912 (2012)
[3] T. Ozaki, et al, Europhys. Lett