Raman light scattering study and microstructural analysis of epitaxial films of the electron-doped superconductor La_{2-x}Ce_{x}CuO_{4}

TL;DR

This study uses temperature-dependent Raman spectroscopy and microstructural analysis to investigate phonon behavior in electron-doped La_{2-x}Ce_{x}CuO_{4} films, revealing interface effects and micro-inclusions influencing superconducting properties.

Contribution

It provides a detailed microstructural and phonon analysis of La_{2-x}Ce_{x}CuO_{4} films, highlighting the role of Cu_{2}O inclusions and interface effects on phonon anomalies near T_c.

Findings

Phonon modes show softening and narrowing below T_c in underdoped films.

Cu_{2}O} inclusions are identified as micron-sized microstructural features.

Interface effects between La_{2-x}Ce_{x}CuO_{4} and Cu_{2}O} may influence phonon anomalies.

Abstract

We present a detailed temperature-dependent Raman light scattering study of optical phonons in molecular-beam-epitaxy-grown films of the electron-doped superconductor La_{2-x}Ce_{x}CuO_{4} close to optimal doping (x ~ 0.08, T_c = 29 K and x ~ 0.1, T_c = 27 K). The main focus of this work is a detailed characterization and microstructural analysis of the films. Based on micro-Raman spectroscopy in combination with x-ray diffraction, energy-dispersive x-ray analysis, and scanning electron microscopy, some of the observed phonon modes can be attributed to micron-sized inclusions of Cu_{2}O. In the slightly underdoped film (x ~ 0.08), both the Cu_{2}O modes and others that can be assigned to the La_{2-x}Ce_{x}CuO_{4} matrix show pronounced softening and narrowing upon cooling below T ~ T_c. Based on control measurements on commercial Cu_{2}O powders and on a comparison to prior Raman scattering studies of other high-temperature superconductors, we speculate that proximity effects at La_{2-x}Ce_{x}CuO_{4}/Cu_{2}O interfaces may be responsible for these anomalies. Experiments on the slightly overdoped La_{2-x}Ce_{x}CuO_{4} film (x ~ 0.1) did not reveal comparable phonon anomalies.