Anisotropic grain-boundary effect on electronic transport in superconducting FeSe thin films

The engineering of the microstructure of a superconducting FeSe thin film by the choice of a proper substrate and its crystallographic orientation is demonstrated. To this end epitaxial c-axis oriented FeSe thin films are grown on (110) oriented single-crystalline SrTiO3 substrates by means of sputtering. The extraordinary microstructure is characterized by the uniaxial alignment of plate-like crystalline grains along the [001](s) substrate direction. The alignment of the elongated grains eventuates in a direction-dependent grain-boundary structure associated with an anisotropic grain-boundary density along the two perpendicular [001](s) and [1 (1) over bar0] s substrate directions. The effect of the grain-boundary structure on the observed anisotropies of the temperature dependent in-plane resistivities and critical current densities in transverse magnetic fields is extensively studied for current transport along [001](s) and [1 (1) over bar0](s).