近日，美国康奈尔大学的Xiaolong Liu及其研究小组取得一项新进展。经过不懈努力，他们成功检测到UTe₂中的配对密度波态。相关研究成果已于2023年6月28日在国际知名学术期刊《自然》上发表。

为了研究UTe₂中的电荷密度波态，该研究小组使用了具有微电子伏特级能量分辨率的超导扫描隧道显微镜（STM）探针来可视化配对能隙。研究人员检测到了三个配对密度波（PDW），每个PDW的峰对峰能隙调制约为10微电子伏特。这些PDW的波矢P_i=1,2,3与之前观察到的电荷密度波（CDW）的波矢Q_i=1,2,3无法区分。通过同时观察UTe₂的超导PDW和非超导CDW，研究人员发现每对P_i:Q_i都呈现出相对的空间相位δ≈π。基于这些观察结果以及考虑到UTe₂是自旋三重态超导体，可以推断该PDW态应为自旋三重态PDW。尽管在超流体³He中存在类似的态，但对于超导体来说，这种态是前所未有的。

据悉，自旋三重态拓扑超导体具有许多前所未有的电子性质，其中包括与量子信息处理相关的分数化电子态。虽然UTe₂可能具有这种体拓扑超导性，但其超导序参量Δ(k)仍未确定。在这种重费米子材料中，Δ(k)的形式多种多样，物理上存在多种可能性。此外，自旋密度波（SDW）、电荷密度波（CDW）和配对密度波（PDW）的交织可能会相互干扰，其中PDW展示出空间调制的超导序参量Δ(r)、电子配对密度和配对能隙。因此，UTe₂中新发现的CDW态引发了PDW态可能存在于该材料中的猜想。

附：英文原文

Title: Detection of a pair density wave state in UTe₂

Author: Gu, Qiangqiang, Carroll, Joseph P., Wang, Shuqiu, Ran, Sheng, Broyles, Christopher, Siddiquee, Hasan, Butch, Nicholas P., Saha, Shanta R., Paglione, Johnpierre, Davis, J. C. Samus, Liu, Xiaolong

Issue&Volume: 2023-06-28

Abstract: Spin-triplet topological superconductors should exhibit many unprecedented electronic properties, including fractionalized electronic states relevant to quantum information processing. Although UTe₂ may embody such bulk topological superconductivity, its superconductive order parameter Δ(k) remains unknown. Many diverse forms for Δ(k) are physically possible in such heavy fermion materials. Moreover, intertwined density waves of spin (SDW), charge (CDW) and pair (PDW) may interpose, with the latter exhibiting spatially modulating superconductive order parameter Δ(r), electron-pair density and pairing energy gap. Hence, the newly discovered CDW state in UTe₂ motivates the prospect that a PDW state may exist in this material. To search for it, we visualize the pairing energy gap with μeV-scale energy resolution using superconductive scanning tunnelling microscopy (STM) tips. We detect three PDWs, each with peak-to-peak gap modulations of around 10μeV and at incommensurate wavevectors P_i=1,2,3 that are indistinguishable from the wavevectors Q_i=1,2,3 of the prevenient CDW. Concurrent visualization of the UTe₂ superconductive PDWs and the non-superconductive CDWs shows that every P_i:Q_i pair exhibits a relative spatial phase δ≈π. From these observations, and given UTe₂ as a spin-triplet superconductor, this PDW state should be a spin-triplet PDW. Although such states do exist in superfluid ³He, for superconductors, they are unprecedented.

DOI: 10.1038/s41586-023-05919-7

Source: https://www.nature.com/articles/s41586-023-05919-7