近日，美国加州大学圣巴巴拉分校Andrea F. Young团队研究了自旋轨道耦合三层石墨烯的超导性和自旋倾斜。2025年5月7日出版的《自然》杂志发表了这项成果。

石墨烯和过渡金属二硫化物平带系统显示出类似的相图，充满了磁性和超导相。一个长期存在的问题是，磁有序化是与超导性竞争还是促进配对。例如，最近在增强自旋轨道耦合的情况下对Bernal双层石墨烯的研究表明，超导态的观察畴和临界温度T_c大幅增加；然而，这种增强的机制仍然未知。 

研究组证明了通过衬底邻近效应在菱面体三层石墨烯（RTG）中引入自旋轨道耦合会产生新的超导袋，用于电子和空穴掺杂，最大T_c ≈ 300 mK比六方氮化硼封装的RTG大三倍。利用局域磁测，研究组发现超导性跨越了具有有限平面内磁矩的自旋倾斜态和具有完全自旋谷锁定的态之间的过渡。这种转变在该Hartree-Fock计算中得到了再现，其中这种转变是由自旋轨道耦合和载流子密度调谐的洪德相互作用之间的竞争驱动的。该实验表明，自旋轨道耦合对超导电性的增强由倾斜角的定量变化驱动，而不是基态对称性的变化。这些结果与最近提出的增强超导性的机制一致，其中自旋倾斜顺序的波动有助于配对相互作用。

附：英文原文 

Title: Superconductivity and spin canting in spin–orbit-coupled trilayer graphene

Author: Patterson, Caitlin L., Sheekey, Owen I., Arp, Trevor B., Holleis, Ludwig F. W., Koh, Jin Ming, Choi, Youngjoon, Xie, Tian, Xu, Siyuan, Guo, Yi, Stoyanov, Hari, Redekop, Evgeny, Zhang, Canxun, Babikyan, Grigory, Gong, David, Zhou, Haoxin, Cheng, Xiang, Taniguchi, Takashi, Watanabe, Kenji, Huber, Martin E., Jin, Chenhao, Lantagne-Hurtubise, tienne, Alicea, Jason, Young, Andrea F.

Issue&Volume: 2025-05-07

Abstract: Graphene and transition metal dichalcogenide flat-band systems show similar phase diagrams, replete with magnetic1,2,3,4,5 and superconducting6,7,8,9,10,11 phases. An abiding question has been whether magnetic ordering competes with superconductivity or facilitates pairing. For example, recent studies of Bernal bilayer graphene in the presence of enhanced spin–orbit coupling show a substantial increase in the observed domain and critical temperature Tc of superconducting states12,13,14; however, the mechanism for this enhancement remains unknown. Here we show that introducing spin–orbit coupling in rhombohedral trilayer graphene (RTG) by substrate proximity effect generates new superconducting pockets for both electron and hole doping, with maximal Tc≈300mK, which is three times larger than in RTG encapsulated by hexagonal boron nitride. Using local magnetometry, we show that superconductivity straddles a transition between a spin-canted state with a finite in-plane magnetic moment and a state with complete spin–valley locking. This transition is reproduced in our Hartree–Fock calculations, in which this transition is driven by the competition between spin–orbit coupling and the carrier-density-tuned Hund’s interaction. Our experiment suggests that the enhancement of superconductivity by spin–orbit coupling is driven by a quantitative change in the canting angle rather than a change in the ground state symmetry. These results align with a recently proposed mechanism for the enhancement of superconductivity15, in which fluctuations in the spin-canting order contribute to the pairing interaction.

DOI: 10.1038/s41586-025-08863-w

Source: https://www.nature.com/articles/s41586-025-08863-w