Epitaxial growth of FeSe${}_{0.5}$Te${}_{0.5}$ thin films on CaF${}_2$ substrates with high critical current density

In-situ epitaxial growth of FeSe${}_{0.5}$Te${}_{0.5}$ thin films is demonstrated on a non-oxide substrate CaF${}_2$. Structural analysis reveals that compressive stress is moderately added to 36-nm thick FeSe${}_{0.5}$Te${}_{0.5}$, which pushes up the critical temperature above 15 K, showing higher values than that of bulk crystals. Critical current density at $T$ = 4.5 K reaches 5.9 x 10${}^4$ Acm${}^{-2}$ at ${\mu }_{0}H$ = 10 T, and 4.2 x 10${}^4$ Acm${}^{-2}$ at ${\mu }_{0}H$ = 14 T. These results indicate that fluoride substrates have high potential for the growth of iron-based superconductors in comparison with popular oxide substrates.