Pulsed-laser deposition of superconducting LiTi2O4 ultrathin films

• Superconducting high-quality LiTi2O4 films were grown by pulsed-laser deposition.
• Growth phase diagram was revealed by varying temperature and target composition.
• Superconducting LiTi2O4 films with thickness as small as 9 nm were realized.

We report epitaxial growth, structural characterizations and thickness-dependent superconducting properties of LiTi2O4 films grown on (111) MgAl2O4 substrates by using pulsed-laser deposition. The variations of growth temperature (Tg) and excess Li composition of target materials were found to be crucial for improving the crystallinity, as verified by X-ray diffraction rocking curve and the in-plane domain configuration. The crystallinity of the desired LiTi2O4 phase improved with increasing Tg, whereas the inclusion of Li-deficient phases became more significant due to high sublimation rate of Li species. The use of the excess Li targets allowed us to elevate Tg up to 750 °C (Li/Ti=1.0) with keeping high crystallinity and phase purity. For films grown under the best condition, the superconducting transition was observed near 12 K even when thickness was as thin as 9 nm.