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

TL;DR

This study investigates the relationship between surface morphology and electronic phase separation in thin film manganites using STM/STS, revealing that surface roughness correlates with phase separation, while flat surfaces are homogeneous.

Contribution

It provides new insights into how surface morphology influences electronic phase separation in manganite thin films, clarifying previous ambiguities from surface-sensitive measurements.

Findings

Rough films exhibit phase separation; flat films are homogeneous.

Surface morphology affects electronic activity at the surface.

No correlation between substrate strain and phase separation.

Abstract

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.