Role of substrates in molecular beam epitaxy growth of superconducting T′-La_2−xCe_xCuO₄ films

We report the molecular beam epitaxy growth of the electron-doped 30-K superconductor, T′-La_2−xCe_xCuO₄. T′-La_2−xCe_xCuO₄ with a very limited range of x can be prepared by bulk synthesis using rather complicated techniques. In contrast, this compound is very easy to prepare by thin film synthesis. The key factor in thin film growth to stabilize T′-La_2−xCe_xCuO₄ is a low synthesis temperature below 700 °C. The use of appropriate substrates further stabilizes T′ formation by an epitaxial effect. In this work, we examined various substrates for the growth of T′-La_2−xCe_xCuO₄. Based on the experimental results, we discuss the roles of substrates.