Eur. Phys. J. B 75, 461-467 (2010)
https://doi.org/10.1140/epjb/e2010-00166-6

Raman light scattering study and microstructural analysis of epitaxial films of the electron-doped superconductor La_2-xCe_xCuO₄

¹ Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, 70569 Stuttgart, Germany
² Physikalisches Institut - Experimentalphysik II, Universität Tübingen, Auf der Morgenstelle 14, 72076 Tübingen, Germany
³ NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, Kanagawa, 243-0198, Japan
⁴ University of New South Wales, School of Physics, 2052 Sydney, New South Wales, Australia
⁵ The Bragg Institute, Australian Nuclear Science and Technology Organization, Lucas Heights, NSW, 2234, Australia

Corresponding author: ^a b.keimer@fkf.mpg.de

Received: 15 February 2010
Revised: 5 May 2010
Published online: 4 June 2010

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-xCe_xCuO₄ 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 Cu₂O. In the slightly underdoped film (x ~ 0.08), both the Cu₂O modes and others that can be assigned to the La_2-xCe_xCuO₄ matrix show pronounced softening and narrowing upon cooling below T ~ T_c. Based on control measurements on commercial Cu₂O powders and on a comparison to prior Raman scattering studies of other high-temperature superconductors, we speculate that proximity effects at La_2-xCe_xCuO₄/Cu₂O interfaces may be responsible for these anomalies. Experiments on the slightly overdoped La_2-xCe_xCuO₄ film (x ~ 0.1) did not reveal comparable phonon anomalies.