The strain effect on the superconducting properties of BaFe2(As, P)2thin films grown by molecular beam epitaxy

BaFe2(As, P)2 thin films were grown by molecular beam epitaxy. Single phase and c-axis oriented thin films were obtained on both LaAlO3 (LAO) and MgO substrates. The critical temperature (Tc) of the thin films grown on LAO substrates showed a P content dependence very similar to single crystals, while those grown on MgO showed a distinctly different dependence. Lattice parameter measurements showed that the thin films grown on MgO were under tensile strain, while no structural deformation was observed for the thin films grown on LAO substrates. The strain effect accounts well for the difference in the P content dependence of Tc. We also obtained the Poisson's ratio from the observed strain, which gave a reasonable value and a systematic change with the P content.