Observation of superconductivity in LaNiO3/La0.7Sr0.3MnO3 superlattice

Abstract

School of Chemistry and Materials Science, Key Laboratory of Magnetic Molecules and Magnetic Information Materials, Ministry of Education, Shanxi Normal University, Linfen 041004, China Atomic scale control of the hetero-interfaces in transition metal oxides has attracted significant attention due to the possibility of observing novel phenomena1,2. The cuprate- and ferrite-based interfacial superconductors have been investigated extensively, while the research of nickelate-based heterostructure is quite rare3,4. Recently Chaloupka and Khaliullin theoretically predicted that antiferromagnetism and high temperature superconductivity (SC) may be stabilized in LNO-based superlattices5. However, the superconductivity state in LNO-based heterostructure has not yet been experimentally reported. In this work, we investigate the properties of a superlattice (SL) composed of an ultrathin LaNiO 3 layer, with a ferromagnetic insulating La 0.7 Sr 0.3 MnO 3 LSMO) layer. Zero resistance and Meissner effect are observed by resistive and magnetic measurements on the superlattice, which gives experimental indication of superconductivity in new kinds of superconductors. X-ray linear dichroism causes the NiO 2 planes to develop electron occupied $x^{2}-y^{2}$ orbital order similar to a cuprate-based superconductor. Our findings demonstrate that artificial interface engineering is a useful way to realize novel physical phenomena, such as superconductivity. Typical x-ray diffraction scans through (002) symmetric reflections of the LNO/LSMO superlattice are shown in Fig. 1a. The main peak of the superlattice and satellite peaks of SL-1 and SL +1 are observed, suggesting sharp interfaces in this superlattice. The coherent epitaxial growth and the absence of secondary phases or dislocations in LNO/LSMO superlattice are both confirmed by high resolution high-angle annular dark field scanning transmission electron microscopy, as shown in Fig. 1b. Because the A site is similar to the superlattice, and the atomic number of B site is contrasted in this image, the LNO layers appear brighter than the LSMO layers The high quality epitaxial [(LNO) 2 /(LSMO) 3 ] 20 superlattice was measured with a current of 5E10-3 mA in a Van der Pauw geometry. In order to directly observe the superconducting property at low temperatures, the temperature dependence of resistivity was measured, as shown in the inset of Fig. 2a. The superlattice displays metallic behavior with the temperature below 10 K and the resistivity abruptly drops around 3.7 K, clearly indicating superconductivity. To further verify the superlattice nature of the observed superconductivity, we measure the magnetic susceptibility (χ) as a function of temperature at magnetic field (H) strength of 10 Oe. As shown in Fig. 2b, the zero field cooled (ZFC) and field cooled (FC) susceptibility are essentially temperature independent at low temperatures. A sharp drop of magnetic susceptibility is observed for both ZFC and FC processes, indicating that the magnetic onset of superconductivity appears around 3.5 K, which is the same as the zero-resistivity temperature. Further confirmation of superconductivity in the superlattice is shown in the inset of Fig. 2b, displaying the typical magnetic hysteresis curve for a superconductor at 2 K after zero-field cooled process. The characteristic M-H loop indicates that the present superlattice is a superconductor of the second kind with a lower critical field of 50 Oe. The work was supported by National Key R&D Program of China (No. 2017YFB0405703), NSFC (Nos. 61434002, 51571136, 11274214), and the Special Funds of Sanjin Scholars Program.