Ferromagnetism and superconductivity are two classic quantum phenomena in solid-state world. They not only remain to be the frontier of fundamental research but also foster important applications, such as data storage and medical imaging. Ferromagnetism and superconductivity are usually incompatible. And it is challenging to merge them in a single material to realize the so-called superconducting ferromagnet or magnetic superconductor. Among the rare cases of superconducting ferromagnets, most possess very low transition temperatures. They may also host only weak coupling between the two antagonistic phenomena. Recently, the research team led by Ding Zhang at Tsinghua University and Qi-Kun Xue at Southern University of Science and Technology reported a superconducting ferromagnetic material with high-temperature superconductivity and nearly room-temperature itinerant ferromagnetism, breaking the world-record. This work, entitled “Lithium Intercalated FeSe as a High-Temperature Superconducting Ferromagnet”, was published online in Nature Communications on August 7.
Figure 1. Schematic of the device and reversible switching between the nonmagnetic low-temperature superconducting state and the high-temperature superconducting ferromagnetic state under electric-field gating.
Figure 2. Materials exhibiting the coexistence of superconductivity and ferromagnetism. Red diamond highlights the high-temperature superconducting ferromagnet reported in this work.
The research team led by Ding Zhang and Qi-Kun Xue has long focused on solid-state ionic tuning of superconductivity, achieving significant advances, including the observation of novel quantum oscillations in the superconducting state [Nat. Commun. 12, 5342 (2021); Nat. Commun. 13, 1316 (2022)] and the exponential decay of vortex entropy [Nat. Commun. 15, 4818 (2024)]. In the latest study, the team collaborated with researchers from Fudan University, Nanjing University, Renmin University of China, and the High Magnetic Field Laboratory in Hefei to systematically modulate and characterize FeSe thin films. After lithium intercalation via electric-field-controlled gating, FeSe films exhibit superconductivity with a critical temperature of 45 K and itinerant ferromagnetism with a Curie temperature exceeding 225 K. The research team is able to reversibly switch between the nonmagnetic low-temperature superconducting state and the high-temperature superconducting ferromagnetic state. Magnetoresistance and Hall resistance display a complex evolution during Cooper-pair condensation. High-resolution spatial imaging using a scanning superconducting quantum interference device (SQUID) confirms the coexistence of superconductivity and ferromagnetism at the micrometer scale. Furthermore, applying a magnetic field to polarize electron spins enhances the superconducting transition temperature, indicative of strong coupling between the ferromagnetic and superconducting states and suggestive of spin-polarized Cooper pairing at a high temperature. Theoretical calculations further indicate that lithium intercalation tend to stabilize a ferromagnetic ground state of FeSe. Among superconducting ferromagnets, lithium-intercalated FeSe exhibits the highest coexisting temperature of superconductivity and itinerant ferromagnetism. It establishes a promising platform for integrating high-temperature superconducting electronics with spintronics, opening potential avenues for novel dissipationless quantum devices.
Yi Hu (PhD student, Tsinghua University), Keyi Liang (PhD student, Fudan University), and Jie Li (PhD student, Nanjing University) are co-first authors of this work. The corresponding authors are Professor Yi Lu (Nanjing University), Professor Yihua Wang (Fudan University), Professor Qi-Kun Xue (Southern University of Science and Technology), and Associate Professor Ding Zhang (Tsinghua University). Other contributors include Professor Hechang Lei and PhD student Fanyu Meng (Renmin University of China), PhD students Zhijie Li and Dr. Ruzhou Zhang (Fudan University), PhD students Jiyuan Wang and Huizhen Wen (Tsinghua University), and Professor Jinglei Zhang and master’s student Jiaqiang Cai (High Magnetic Field Laboratory, HFIPS, Chinese Academy of Sciences).
At the 30th International Conference on Low Temperature Physics, held recently in Bilbao, Spain, Yi Hu’s poster presenting this research was recognized as one of the Best Poster Awards.
DOI: https://doi.org/10.1038/s41467-025-62624-x
