  High critical current densities Jc of 4 MA/cm2 at 4 K were obtained in
Co-doped BaFe2As2 (BaFe2As2:Co) epitaxial films grown directly on (La, Sr)(Al,
Ta)O3 substrates by pulsed laser deposition. Use of a highly pure target and
improvement of film homogeneity were the critical factors to achieve the high
Jc. The improved BaFe2As2:Co epitaxial films contained almost no Fe impurity
and showed high crystallinity (crystallite tilt angle delta omega = 0.5 deg and
twist angle delta fai = 0.5 deg) and a sharp superconducting transition with a
width of 1.1 K. It is considered that these improvements resulted in the
enhanced superconducting properties comparable to those of single crystals.
