EN
[1].The spinel oxide system has many novel intrinsic properties, which has attracted a lot of attention. At present, superconductivity has been found in two spinel oxides, LiTi2O4 and MgTi2O4.They both belong to the normal spinel structure with a general formula, AB2O4 (space group Fd-3m）.A crystal cell of AB2O4 has 32 oxygen ions, forming 64 tetrahedra sites and 32 octahedra sites. Among them, 8 sites are occupied by A ions(8a equivalent positions), and 16 sites are occupied by B ions(16d equivalent positions ). Our group has prepared high quality LiTi2O4 superconducting films ,MgTi2O4 single-component superconducting films and [MgTi2O4/SrTiO3]2 superlattices.
A.LiTi2O4
a.Structure characterization
(1) θ-2θ scan reveals that the diffraction pattern only includes the peaks of the (l l l)-oriented MgAl2O4 substrate and the corresponding (l l l)-oriented LTO film, as no impurity exists in the sample[1].
The variation of Ce doping levels with changing the position in the combinatorial film: the nominal Ce doping changes continuously from 0.1 to 0.19 on a SrTiO3 substrate [2].
（3) The 2D reciprocal space mapping of the (404) plane demonstates the high quality of the film[1].
b.Electrical transport measurements
A Tc0 of up to ~13 K has been obtained [1].
c. Evolution from superconducting to insulating phase by changing the oxygen pressure
The RRR and lattice parameters of Li1+xTi2-xO4 thin films can be continuously tuned by changing the oxygen pressure during deposition, and the evolution from superconducting LiTi2O4 phase to insulating Li4Ti5O12 phase can also be observed[2].
d. Characterization of surface morphology
The surface morphology of LiTi2O4 thin films with different orientations has been checked by atomic force microscopy (AFM). It is found that all of them have smooth surface[1].
B.MgTi2O4
a. Structure characterization
（1) θ/2θ scan results of MTO thin films. There are only (00l)-oriented peaks of MTO and MAO, demonstrating that no impurity presents in our samples[3].
(2) the peak full-width a thalf-maximum(FWHM) is 1.70°, it shows that MTO thin films has good crystallinity[3]
(3)The φ scans of the (044) plane.There are four peaks of nearly equal height, reflecting the relatively good epitaxy of the samples[3].
By engineering the [MgTi2O4/SrTiO3]2 superlattice,
the zero resistance has been achieved at 3K, and the onset transition temperature is up to 5K.
Temperature dependence of magnetization of the [MgTi2O4/SrTiO3]2 superlattice at 0.5mT with and without field cooling indicates that the superconductivity can be achieved above 3K[4].
More
Y. L. Jia, The preparation and study on physical properties of transition metal oxide superconducting films, Ph.D. Thesis, Institute of Physics Chinese Academy of Sciences (2018)- Y. L. Jia, G. He, W. Hu, H. Yang, Z. Z. Yang, H. S. Yu and K. Jin, The effects of oxygen in spinel oxide Li1+xTi2-xO4-δ thin films, Sci. Rep. 8, 3995 (2018)
- W. Hu, Researches on the superconducting properties of electron-doped cuprates and spinel oxide superconductors, Ph.D. Thesis, Institute of Physics Chinese Academy of Sciences (2019)
- W. Hu, Z. P Feng, B. C. Gong, G. He, D. Li and K. Jin, Emergent superconductivity in single-crystalline MgTi2O4 films via structural engineering,Phys. Rev. B 101, 220510(R) (2020).