Strongly correlated superconductivity in a copper-based metal-organic framework with a perfect kagome lattice

T Takenaka; K Ishihara; M Roppongi; Y Miao; Y Mizukami; T Makita; J Tsurumi; S Watanabe; J Takeya; M Yamashita; K Torizuka; Y Uwatoko; T Sasaki; X Huang; W Xu; D Zhu; N Su; J-G Cheng; T Shibauchi; K Hashimoto

doi:10.1126/sciadv.abf3996

Strongly correlated superconductivity in a copper-based metal-organic framework with a perfect kagome lattice

Sci Adv. 2021 Mar 17;7(12):eabf3996. doi: 10.1126/sciadv.abf3996. Print 2021 Mar.

Authors

T Takenaka¹, K Ishihara¹, M Roppongi¹, Y Miao¹, Y Mizukami¹, T Makita¹, J Tsurumi¹, S Watanabe¹, J Takeya¹, M Yamashita², K Torizuka^{2

3}, Y Uwatoko², T Sasaki⁴, X Huang⁵, W Xu⁵, D Zhu⁵, N Su⁶, J-G Cheng⁶, T Shibauchi⁷, K Hashimoto⁷

Affiliations

¹ Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan.
² Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan.
³ Department of Physics, Nippon Institute of Technology, Miyashiro, Saitama 345-8501, Japan.
⁴ Institute for Materials Research, Tohoku University, Aoba-ku, Sendai 980-8577, Japan.
⁵ Beijing National Laboratory for Molecular Sciences, Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
⁶ Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
⁷ Department of Advanced Materials Science, University of Tokyo, Kashiwa, Chiba 277-8561, Japan. shibauchi@k.u-tokyo.ac.jp k.hashimoto@edu.k.u-tokyo.ac.jp.

Abstract

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 T _c 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.

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