Orbital order and anisotropic transport properties in doped manganites induced by epitaxial coherency strain

Epitaxial coherency strain is a crucial parameter strongly influencing the complex interplay between structure as well as spin, charge, and orbital degrees of freedom in the doped manganites. We have grown epitaxial manganite thin films on various substrates using ultrahigh vacuum laser molecular beam epitaxy with RHEED control. In order to study transport perpendicular to the film plane, mesa structures have been fabricated into the epitaxial films. For coherently strained $La2/3Ca1/3MnO3$ and $La2/3Ba1/3MnO3$ thin films grown on $SrTiO3$ and $NdGaO3$ substrates, an unusual transport anisotropy is observed. Whereas metallic behavior is found within the plane of biaxial coherency strain, for transport perpendicular to this plane an insulating behavior and nonlinear current–voltage characteristics are observed. This behavior can be interpreted in terms of a strain induced orbital order effect at fixed doping. Our results demonstrate the effect of epitaxial coherency strain in heterostructures required for magnetoelectronic devices.