Local electronic transport in La0.7Sr0.3MnO3 thin films studied by scanning tunneling potentiometry

We have used a scanning tunneling microscope in potentiometry mode to investigate the local electric potential distribution in current carrying epitaxial La0.7Sr0.3MnO3 thin films, with magnetotransport properties similar to the ones of single crystals. Scans imaging simultaneously the surface topography and the potential distribution have been obtained with an unprecedented resolution. In textured La0.7Sr0.3MnO3/MgO, sharp potential steps coincide with some of the grain boundaries, whereas other grains are electrically well connected. The precise nature of the local electronic transport, the percolation of the current through the grain network, and the existence of phase separated insulating domains are then discussed.