美国加州理工学院Stevan Nadj-Perge团队研究了铁基超导体中的库珀对密度调制态。该项研究成果发表在2025年3月19日出版的《自然》杂志上。

超导（SC）状态打破了底层晶体的空间群对称性，可以表现出序参数的非平凡空间调制。以前，这种状态与平移对称性的破坏密切相关，导致密度波阶，波长跨越几个晶胞。然而，一个相关的基本概念长期以来一直被忽视：当只有空间群的晶胞内对称性被打破时，SC态可以表现出一种独特的非平凡调制，保持长程晶格平移。

研究组将这一新概念称为对密度调制（PDM），并报告了铁基超导体FeTe_0.55Se_0.45剥落薄片中PDM状态的首次观察。使用扫描隧道显微镜（STM），发现了稳健的SC间隙调制，其波长对应于晶格周期性，振幅超过间隙平均值的30%。值得注意的是，研究组发现观察到的调制源于两个名义上等效的铁子晶格上SC间隙的巨大差异。

实验结果得到了模型计算的支持，表明与密度波阶相反，PDM状态是由子晶格对称性断裂和薄片特有的向列畸变相互作用驱动的。该研究结果为探索强关联电子系统中的交织序开辟了新的前沿，并为铁基超导体翻开了新的篇章。

附：英文原文

Title: Cooper-pair density modulation state in an iron-based superconductor

Author: Kong, Lingyuan, Papaj, Micha, Kim, Hyunjin, Zhang, Yiran, Baum, Eli, Li, Hui, Watanabe, Kenji, Taniguchi, Takashi, Gu, Genda, Lee, Patrick A., Nadj-Perge, Stevan

Issue&Volume: 2025-03-19

Abstract: Superconducting (SC) states that break space-group symmetries of the underlying crystal can exhibit nontrivial spatial modulation of the order parameter. Previously, such states were intimately associated with the breaking of translational symmetry1,2, resulting in the density-wave orders3,4,5,6,7,8, with wavelengths spanning several unit cells9,10,11,12,13,14,15,16,17,18,19. However, a related basic concept has long been overlooked20: when only intra-unit-cell symmetries of the space group are broken, the SC states can show a distinct type of nontrivial modulation preserving long-range lattice translation. Here we refer to this new concept as the pair density modulation (PDM) and report the first observation of a PDM state in exfoliated thin flakes of the iron-based superconductor FeTe0.55Se0.45. Using scanning tunnelling microscopy (STM), we discover robust SC gap modulation with the wavelength corresponding to the lattice periodicity and the amplitude exceeding 30% of the gap average. Notably, we find that the observed modulation originates from the large difference in SC gaps on the two nominally equivalent iron sublattices. The experimental findings, backed up by model calculations, suggest that, in contrast to the density-wave orders, the PDM state is driven by the interplay of sublattice symmetry breaking and a peculiar nematic distortion specific to the thin flakes. Our results establish new frontiers for exploring the intertwined orders in strong-correlated electronic systems and open a new chapter for iron-based superconductors.

DOI: 10.1038/s41586-025-08703-x

Source: https://www.nature.com/articles/s41586-025-08703-x