超伝導と磁性を同時に持つ新物質を発見（MIT Physicists Discover New Type of Superconductor That Is Also a Magnet）

2025-05-22 マサチューセッツ工科大学（MIT）

An illustration depicts pairs of superconducting electrons in rhombohedral graphene (the middle lattice structure) that spin in clockwise or counterclockwise direction (corresponding to blue and red colors). The electron pairs exhibit properties of magnetism and superconductivity that were not thought to co-exist in one material. The electronic state represents a new form of magnetic superconductor. Credits:Image credit: Sampson Wilcox, Research Laboratory of Electronics

＜関連情報＞

• https://news.mit.edu/2025/mit-physicists-discover-new-type-superconductor-also-magnet-0522
• https://www.nature.com/articles/s41586-025-09169-7

菱面体晶グラフェンにおけるキラル超伝導の兆候 Signatures of chiral superconductivity in rhombohedral graphene

Tonghang Han,Zhengguang Lu,Zach Hadjri,Lihan Shi,Zhenghan Wu,Wei Xu,Yuxuan Yao,Armel A. Cotten,Omid Sharifi Sedeh,Henok Weldeyesus,Jixiang Yang,Junseok Seo,Shenyong Ye,Muyang Zhou,Haoyang Liu,Gang Shi,Zhenqi Hua,Kenji Watanabe,Takashi Taniguchi,Peng Xiong,Dominik M. Zumbühl,Liang Fu & Long Ju
Nature  Published:22 May 2025
DOI:https://doi.org/10.1038/s41586-025-09169-7

We are providing an unedited version of this manuscript to give early access to its findings. Before final publication, the manuscript will undergo further editing. Please note there may be errors present which affect the content, and all legal disclaimers apply.

Abstract

Chiral superconductors are unconventional superconducting states that break time reversal symmetry spontaneously and typically feature Cooper pairing at non-zero angular momentum. Such states may host Majorana fermions and provide an important platform for topological physics research and fault-tolerant quantum computing^1–7. Despite intensive search and prolonged studies of several candidate systems^8–26, chiral superconductivity has remained elusive so far. Here we report the discovery of robust unconventional superconductivity in rhombohedral tetra- and penta-layer graphene without moiré superlattice effects. We observed two superconducting states in the gate-induced flat conduction bands with T_c up to 300 mK and charge density n_e down to 2.4*10¹¹ cm^-2 in five devices. Spontaneous time-reversal-symmetry-breaking due to electron’s orbital motion is found, and several observations indicate the chiral nature of these superconducting states, including: 1. In the superconducting state, R_xx shows magnetic hysteresis in varying out-of-plane magnetic field B_⊥—absent from all other superconductors; 2. the superconducting states are robust against in-plane magnetic field and are developed within a spin- and valley-polarized quarter-metal phase; 3. the normal states show anomalous Hall signals at zero magnetic field and magnetic hysteresis. We also observed a critical B_⊥ of 1.4 Tesla, higher than any graphene superconductivity and indicates a strong-coupling superconductivity close to the BCS-BEC crossover²⁷. Our observations establish a pure carbon material for the study of topological superconductivity, with the promise to explore Majorana modes and topological quantum computing.