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A research team co-led by Dr. Qiaoshi Zeng of the Center for High Pressure Science and Technology Advanced Research (HPSTAR) and Prof. Junjie Zhang of Shandong University has achieved significant progress in bilayer nickelates. In high-quality single crystals of La₂SmNi₂O₇₋ₓ, they realized bulk superconductivity with a transition temperature as high as 96 K under high pressure—setting a new record for the highest Tc (critical temperature) among all nickel-based superconductors to date. The findings were published in Nature under the title “Bulk superconductivity up to 96 K in pressurized nickelate single crystals.”
The discovery in 2023 of ~80 K superconductivity under high pressure in the bilayer nickelate La₃Ni₂O₇, made nickelates have rapidly emerged as a new frontier in high-temperature superconductivity research, following cuprates and iron-based superconductors as the third class of unconventional high-Tc materials. They are also the second class of superconductors after cuprates to exceed the liquid-nitrogen temperature range, opening new opportunities for fundamental research and potential applications, and fueling intense worldwide research interest. However, growing high-quality bulk nickelate single crystals requires stringent conditions, and superconductivity in these materials typically appears only under high pressures, posing major challenges for discovering new nickelate superconductors.
The team successfully introduced an ambient-pressure flux-growth method for preparing nickelate single crystals and, for the first time, grew high-quality, structurally uniform La₂SmNi₂O₇₋ₓ single crystals nearly 200 μm in size. Compared with traditional high-oxygen-pressure growth, the ambient-pressure flux method offers multiple advantages: simpler equipment, higher crystal purity, fewer impurity phases, improved structural integrity, better reproducibility, and easier control of oxygen content. In particular, the introduction of Sm, which has a smaller ionic radius, provides “chemical pressure” that effectively reduces stacking faults and structural defects, greatly enhancing overall crystal quality.
Electrical transport and magnetic susceptibility measurements on single crystals at ultrahigh pressures is one of the most technically challenging tasks in high-pressure research. After years of targeted technical development, Dr. Zeng’s group at HPSTAR has established reliable techniques for in-situ electrical transport and DC magnetization measurements under nearly hydrostatic ultrahigh pressures. Using helium as a hydrostatic pressure-transmitting medium, the team conducted in-situ high-pressure, low-temperature transport and magnetization measurements on La₂SmNi₂O₇₋ₓ crystals. At around 21 GPa, they clearly observed a superconducting transition up to 96 K, zero resistance at 73 K, and a pronounced Meissner effect at 60 K, strong evidence of robust bulk Tc superconductivity in this new material. Further in-situ synchrotron X-ray diffraction measurements under high pressure and low temperature revealed that superconductivity exists in both monoclinic and tetragonal phases, indicating that the superconducting state may not rely on a specific lattice symmetry, an important clue toward understanding its mechanism.
Moreover, by comparing results across a series of samples, the team identified an empirical rule that may guide the design of higher-Tc nickelate superconductors: the larger the in-plane lattice distortion at room temperature, the higher the superconducting transition temperature under pressure. Guided by this principle, they developed La₂SmNi₂O₇₋ₓ and achieved a record Tc of 96 K. This is the highest Tc ever achieved in a nickel-based superconductor and is the first time a nickelate has approached the “100 K” threshold, marking a major milestone. This breakthrough represents a significant step forward in the development of new high-Tc superconducting materials and provides valuable guidance for exploring superconducting mechanisms and designing nickelates with even higher Tc.
PhD students Li Feiyu (Shandong University) and Xing Zhenfang (HPSTAR) are the paper’s co-first authors. Dr. Zeng Qiaoshi of HPSTAR and Shanghai Advanced Research in Physical Sciences (SHARPS), Dr. Peng Di of SHARPS, and Profs. Zhang Junjie and Tao Xutang of Shandong University are the corresponding authors. Additional contributors from HPSTAR include scientist Dr. Zhidan Zeng and PhD students Liu Yuxin and Luo Tao. This work was supported by the Ministry of Science and Technology of China, the National Natural Science Foundation of China, the Chinese Academy of Sciences, and the Shanghai Science and Technology Commission. The in-situ high-pressure diffraction experiments were supported by the 17U beamline of the Shanghai Synchrotron Radiation Facility and the in-situ high-pressure and low-temperature diffraction experiments were supported by the 10XU beamline at Spring8, Japan.
Caption: Pressure-induced superconductivity in La₂SmNi₂O7₋ single crystals. a. Zero-resistance at 21.6 GPa under magnetic fields. b. Pronounced Meissner effect observed at 20.6 GPa；c. The relationship between the transition temperature Tc and in-plane lattice distortion at ambient conditions.
北京高压科学研究中心（HPSTAR）的曾桥石研究员团队与山东大学的张俊杰教授团队合作，在双层镍酸盐体系中取得了重要进展：在高质量的La₂SmNi₂O7-d单晶中, 通过高压诱导实现了高达 96 K 的体超导转变，创造了迄今镍基超导体的最高转变温度的纪录。研究成果以《Bulk superconductivity up to 96 K in pressurized nickelate single crystals》为题发表于Nature
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