We report direct evidence of the theoretically predicted electron-rich surface of doped perovskite manganites ${\mathrm{La}}_{0.7}{A}_{0.3}{\mathrm{MnO}}_3(A=\text{Ca}$, Sr) by means of surface-enhanced Raman spectroscopy. The required Au nanoparticles were grown on top of thin manganite films by the metalorganic aerosol deposition technique, which provides a stable oxygen atmosphere and prevents deoxygenation effects. The acquired surface-enhanced Raman spectra of rhombohedral ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3$ thin films reveal the symmetry-forbidden Jahn-Teller stretching modes demonstrating the predicted symmetry breaking at the surface and fallback into the orthorhombic (Pnma) structure. This results in a unique Jahn-Teller reconstructed surface structure, which limits the capabilities of mixed-valence manganites in spintronic applications, but will be highly favorable for catalytic reactions.

• Received 20 November 2018
• Revised 30 April 2019

DOI:https://doi.org/10.1103/PhysRevMaterials.3.060401

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Published by the American Physical Society