Superconductivity in Freestanding Infinite-Layer Nickelate Membranes

发布者:沈允育发布时间:2024-06-21浏览次数:10


Recently, Prof. Yuefeng Nie's group successfully synthesized high-quality superconducting freestanding infinite-layer nickelate membranes by using oxide molecular beam epitaxy (OMBE) combined with a growth and transfer method. Given the high lattice tunability of freestanding membranes, this work provides new opportunities to explore the superconductivity in nickelates by applying extreme strain and constructing artificial heterostructures. The article entitled "Superconductivity in freestanding infinite-layer nickelate membranes" was recently published in Advanced Materials (https://doi.org/10.1002/adma.202402916).

Infinite-layer nickelates share similar crystal structures and electronic configurations with cuprate superconductors but also exhibit significant differences, providing new opportunities to uncover the mechanism of unconventional high-temperature superconductivity. However, the synthesis of superconducting infinite layer nickelates is extremely challenging, and the superconducting phase has only been observed in epitaxial thin films. To obtain the superconducting infinite-layer structure phase (RNiO2), it is vital to grow high-quality perovskite precursor phases (RNiO3) and then remove the apical oxygen atoms through topotactic reduction. Due to the large difference in the lattice constants between the perovskite precursor phase and the infinite-layer structure phase, the choice of substrates for epitaxial growth is limited, hindering the extent of strain modulation. Compared to epitaxial thin films and bulk materials, freestanding membranes allow a much wider range of strain modulation and enable heterostructure stacking for exploring the pairing symmetry in nickelates. However, both the demanding growth requirements for the perovskite precursor phase and the metastable property of the reduced infinite-layer phase pose significant challenges for the preparation of superconducting freestanding infinite-layer nickelate membranes.

In this work, the research group utilized OMBE to engineer the interface chemical composition with atomic precision, addressing the aforementioned difficulties. A SrTiO3 (STO) buffer layer was introduced to prevent interdiffusion between the water-soluble sacrificial layer Sr4Al2O7 and the perovskite precursor phase La0.8Sr0.2NiO3. An extra [LaO] layer was deposited on the TiO2-terminated STO buffer layer, suppressing the formation of impurity phases and improving the crystalline quality of the perovskite precursor phase. Then, the infinite-layer structure phase was obtained through topotactic reduction. In the transfer process, instead of the commonly used water-soluble sacrificial layer Sr3Al2O6, a newly developed water-soluble layer Sr4Al2O7 with high efficiency (dissolution rate is approximately 10 times that of Sr3Al2O6) was utilized. Combined with a room-temperature electrode transfer technique, sample degradation and oxygen backfilling were greatly minimized. Based on these advancements, superconducting freestanding infinite-layer nickelate membranes were successfully prepared, providing a new platform to explore superconductivity in infinite-layer nickelates.

The co-first authors, Shengjun Yan, Wei Mao and Wenjie Sun, contributed to this work equally. Prof. Yuefeng Nie is the corresponding author. Dr. Haoying Sun and Dr. Yueying Li have made important contributions to this research. This work has also received support from Prof. Zhengbin Gu and Prof. Peng Wang. This work received funding support from the National Key R&D Program of China and the National Natural Science Foundation of China.