Superconducting T′-La2-xCexCuO4 films grown by molecular beam epitaxy

In this letter we report the synthesis of superconducting T'-La2-xCexCuO4 on SrTiO3(001) by molecular beam epitaxy. Although T'-La2-xCexCuO4 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 SrTiO3 substrates, which seems to stabilize the formation of the T' structure by an epitaxial effect. The best T-c was similar to 30 K by onset and similar to 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)CuO4 or (Pr, Ce)(2)CuO4 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.