Structural phase control of (La${}_{1.48}$Nd${}_{0.40}$Sr${}_{0.12}$)CuO${}_4$ thin films by epitaxial growth technique

Epitaxial growth of (La${}_{1.48}$Nd${}_{0.40}$Sr${}_{0.12}$)CuO${}_4$ thin films was studied by pulsed-laser deposition technique on three different substrates, SrTiO${}_3$ (100), LaSrAlO${}_4$ (001), and YAlO${}_3$ (001). The (Nd,Sr,Ce)${}_2$CuO${}_4$-type structure appears at the initial growth stage on SrTiO${}_3$ (100) when the film is deposited under the growth conditions optimized for (La,Sr)${}_2$CuO${}_4$. This (Nd,Sr,Ce)${}_2$CuO${}_4$-type structure can be eliminated by increasing the substrate temperature and the laser repetition frequency. Films on LaSrAlO${}_4$ (001) maintain a La${}_2$CuO${}_4$-type structure as bulk samples, but those on YAlO${}_3$ (001) show phase separation into La${}_2$CuO${}_4$- and Nd${}_2$CuO${}_4$-type structures. Such complicated results are explained in terms of the competition between lattice misfit and thermodynamic conditions. Interestingly the films with La${}_2$CuO${}_4$-type structure prepared on SrTiO${}_3$ and LaSrAlO${}_4$ show different surface structures and transport properties. The results indicate the possibility of controlling charge stripes of (La${}_{1.48}$Nd${}_{0.40}$Sr${}_{0.12}$)CuO${}_4$ as was demonstrated in (La,Ba)${}_2$CuO${}_4$ thin films by Sato et al. (Phys. Rev. B {\bf 62}, R799 (2000)).