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 $\mu_0H$ = 10 T, and 4.2 x 10$^4$ Acm$^{-2}$ at $\mu_0H$ = 14 T. These results indicate that fluoride substrates have high potential for the growth of iron-based superconductors in comparison with popular oxide substrates. 
I. Tsukada, M. Hanawa, T. Akiike, F. Nabeshima, Y. Imai, A. Ichinose,   S. Komiya, T. Hikage, T. Kawaguchi, H. Ikuta, and A....
cond-mat.supr-con cond-mat.mtrl-sci