Metal-organic frameworks (MOFs), which are self-assemblies of metal ions and organic ligands, provide a tunable platform to search a new state of matter. A two-dimensional (2D) perfect kagome lattice, whose geometrical frustration is a key to realizing quantum spin liquids, has been formed in the π-d conjugated 2D MOF [Cu3(C6S6)]n (Cu-BHT). The recent discovery of its superconductivity with a critical temperature Tc of 0.25\,kelvin raises fundamental questions about the nature of electron pairing. Here, we show that Cu-BHT is a strongly correlated unconventional superconductor with extremely low superfluid density. A nonexponential temperature dependence of superfluid density is observed, indicating the possible presence of superconducting gap nodes. The magnitude of superfluid density is much smaller than those in conventional superconductors, and follows the Uemura's relation of strongly correlated superconductors. These results imply that the unconventional superconductivity in Cu-BHT originates from electron correlations related to spin fluctuations of kagome lattice.
@article{arxiv.2103.15607,
title = {Strongly correlated superconductivity in a copper-based metal-organic framework with a perfect kagome lattice},
author = {T. Takenaka and K. Ishihara and M. Roppongi and Y. Miao and Y. Mizukami and T. Makita and J. Tsurumi and S. Watanabe and J. Takeya and M. Yamashita and K. Torizuka and Y. Uwatoko and T. Sasaki and X. Huang and W. Xu and D. Zhu and N. Su and J. -G. Cheng and T. Shibauchi and K. Hashimoto},
journal= {arXiv preprint arXiv:2103.15607},
year = {2021}
}