Correlations between the morphology and the electronic structure at the surface of thin film manganites, investigated with STM

Thin-film colossal magnetoresistance manganites such as La$_{0.67}$Ca$_{0.33}$MnO$_{3}$ (LCMO) have now been intensely studied for more than a decade, but the issue of possible nanoscale electronic phase separation is not fully solved. Scanning Tunneling Microscopy / Spectroscopy (STS) has been pivotal in studying phase separation, but is hindered by being surface- rather than bulk-sensitive. For our sputtered LCMO films the data indicates a strong correlation between surface morphology and signatures of phase separation; rough films show phase separation while atomically flat films are electronically homogeneous but have a more or less inactive surface layer. Regardless of surface morphology, the film bulk is electronically and magnetically active. Many of the reported conclusions about electronic inhomogeneities measured by STS have been confused by this issue. We study both strained and unstrained films and find no correlation between substrate-induced strain and either electronic phase separation or dead layers.