Despite of the various forms of superconductivity, conventional or unconventional, topologically trivial or nontrivial, the condensation of charge-2e Cooper pairs has remained the origin and character of all superconductivity, as described by the BCS theory. We report our experimental discoveries of the charge-4e and charge-6e superconductivity in ultrathin ring devices fabricated using the kagome superconductor CsV3Sb5 [1]. These new phase coherent states are discovered by the observation of the quantized magnetic flux in units of h/4e and h/6e in systematic magneto-transport measurements. Our observations provide direct experimental evidence for the existence of phase coherent paired quantum matter beyond the charge-2e superconductors, and provide ground work for exploring the physical properties of the charge-4e and charge-6e superconductivity as unprecedented phases of matter beyond the condensation of Cooper pairs described by the BCS theory.
[1] Jun Ge#, Pinyuan Wang#, Ying Xing, Qiangwei Yin, Anqi Wang, Jie Shen, Hechang Lei, Ziqiang Wang, and Jian Wang*. "Charge-4e and Charge-6e Flux Quantization and Higher Charge Superconductivity in Kagome Superconductor Ring Devices" Physical Review X 14, 021025 (2024) (arXiv: 2201.10352). (The paper was selected as “Featured in Physics” by the editor of Physical Review X, with an accompanying VIEWPOINT article entitled “Cooper Pairs Pair Up in a Kagome Metal” (link to the accompanying paper: https://physics.aps.org/articles/v17/80). Prof. Chandra M. Varma, a recipient of the John Bardeen Prize, highlighted this work in the Journal Club for Condensed Matter Physics. Link: DOI: 10.36471/JCCM_March_2022_03.)
Figure 1. Higher charge superconductivity in kagome superconductor ring devices.