Superconducting T^′-La_2-xCe_xCuO₄ Films Grown by Molecular Beam Epitaxy

Abstract

In this letter we report the synthesis of superconducting T ′ -La 2- x Ce x CuO 4 on SrTiO 3 (001) by molecular beam epitaxy. Although T ′ -La 2- x Ce x CuO 4 with a very limited range of x can be prepared by bulk synthesis using rather complicated techniques, this compound is very easy to obtain by thin film synthesis. Crucial to our success was the use of SrTiO 3 substrates, which seems to stabilize the formation of the T ′ structure by an epitaxial effect. The best T c was ∼30 K by onset and ∼28 K by zero resistance, which was obtained for x =0.109. The resistivity showed a metallic temperature dependence, and the film's overall behavior was similar to that for the best (Nd, Ce) 2 CuO 4 or (Pr, Ce) 2 CuO 4 films. Moreover, the single phase of the T ′ structure formed for a composition range of 0.09< x <0.22, which is much wider than for previously reported bulk synthesis.