Spinel compounds have demonstrated rich functionalities but rarely shown superconductivity. Here, we report the emergence of superconductivity in the spinel MgTi2O4, known to be an insulator with a complicated order. The superconducting transition is achieved by engineering a superlattice of MgTi2O4 and SrTiO3. The onset transition temperature in the MgTi2O4 layer can be tuned from 0 to 5 K in such geometry, concurrently with a stretched c-axis (from 8.51 to 8.53 \AA) compared to the bulk material. Such a positive correlation without saturation suggests ample room for the further enhancement. Intriguingly, the superlattice exhibits isotropic upper critical field Hc2 that breaks the Pauli limit, distinct from the highly anisotropic feature of interface superconductivity. The origin of superconductivity in the MgTi2O4 layer is understood in combination with the electron energy loss spectra and the first-principles electronic structure calculations, which point to the birth of superconductivity in the MgTi2O4 layer by preventing the Ti-Ti dimerization. Our discovery not only provides a platform to explore the interplay between the superconductivity and other exotic states, but also opens a new window to realize superconductivity in the spinel compounds as well as other titanium oxides.
@article{arxiv.1905.08641,
title = {Emergent superconductivity in single crystalline $\mathrm{MgTi}_2\mathrm{O}_4$ films via structural engineering},
author = {Wei Hu and Zhongpei Feng and Ben-Chao Gong and Ge He and Dong Li and Mingyang Qin and Yujun Shi and Qian Li and Qinghua Zhang and Jie Yuan and Beiyi Zhu and Kai Liu and Tao Xiang and Lin Gu and Fang Zhou and Xiaoli Dong and Zhongxian Zhao and Kui Jin},
journal= {arXiv preprint arXiv:1905.08641},
year = {2020}
}