Cao Lu, Xue Yucheng, Wang Yingbo, Zhang Fu-Chun, Kang Jian, Gao Hong-Jun, Mao Jinhai, Jiang Yuhang
College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing, 100049, China.
School of Physical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
Nat Commun. 2024 Aug 22;15(1):7234. doi: 10.1038/s41467-024-51558-5.
Pair density wave (PDW) is a distinct superconducting state characterized by a periodic modulation of its order parameter in real space. Its intricate interplay with the charge density wave (CDW) state is a continuing topic of interest in condensed matter physics. While PDW states have been discovered in cuprates and other unconventional superconductors, the understanding of diverse PDWs and their interactions with different types of CDWs remains limited. Here, utilizing scanning tunneling microscopy, we unveil the subtle correlations between PDW ground states and two distinct CDW phases - namely, anion-centered-CDW (AC-CDW) and hollow-centered-CDW (HC-CDW) - in 2H-NbSe. In both CDW regions, we observe coexisting PDWs with a commensurate structure that aligns with the underlying CDW phase. The superconducting gap size, Δ(r), related to the pairing order parameter is in phase with the charge density in both CDW regions. Meanwhile, the coherence peak height, H(r), qualitatively reflecting the electron-pair density, exhibits a phase difference of approximately 2π/3 relative to the CDW. The three-fold rotational symmetry is preserved in the HC-CDW region but is spontaneously broken in the AC-CDW region due to the PDW state, leading to the emergence of nematic superconductivity.
配对密度波（PDW）是一种独特的超导态，其特征在于序参量在实空间中的周期性调制。它与电荷密度波（CDW）态之间复杂的相互作用一直是凝聚态物理中备受关注的话题。虽然在铜酸盐和其他非常规超导体中已发现PDW态，但对各种PDW及其与不同类型CDW相互作用的理解仍然有限。在此，利用扫描隧道显微镜，我们揭示了2H-NbSe₂中PDW基态与两种不同的CDW相——即以阴离子为中心的CDW（AC-CDW）和以空穴为中心的CDW（HC-CDW）——之间的微妙关联。在两个CDW区域中，我们观察到具有与底层CDW相匹配结构的共存PDW。与配对序参量相关的超导能隙大小Δ(r)在两个CDW区域中均与电荷密度同相。同时，定性反映电子对密度的相干峰高度H(r)相对于CDW呈现出约2π/3的相位差。三重旋转对称性在HC-CDW区域得以保留，但在AC-CDW区域由于PDW态而自发破缺，导致向列型超导的出现。
