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.

Chiral spin-triplet superconductivity is a topologically nontrivial pairing state with broken time-reversal symmetry, which can host Majorana quasiparticles [1,2]. The recently discovered heavy-fermion superconductor UTe 2 [3] exhibits peculiar properties of spin-triplet pairing [3][4][5][6], and the possible chiral state has been actively discussed [7][8][9]. However, the symmetry and nodal structure of its order parameter in the bulk, which determine the Majorana surface states [2],remains controversial [10][11][12][13]. Here we focus on the number and positions of superconducting gap nodes in the ground state of UTe 2 . Our magnetic penetration depth measurements for three field orientations in the Meissner state reveal the power-law temperature dependence with exponents less than 2, which excludes single-component spin-triplet states. The anisotropy of low-energy quasiparticle excitations indicates multiple point nodes near the k y -and k z -axes, evidencing that the order parameter has multiple components in a chiral complex form. We find that most consistent is a chiral B 3u + iA u non-unitary state, which provides fundamentals of the topological properties in UTe 2 .

Chiral spin-triplet superconductivity is a topologically nontrivial pairing state with broken time-reversal symmetry, which can host Majorana quasiparticles. The heavy-fermion superconductor UTe2 exhibits peculiar properties of spin-triplet pairing, and the possible chiral state has been actively discussed. However, the symmetry and nodal structure of its order parameter in the bulk, which determine the Majorana surface states, remains controversial. Here we focus on the number and positions of superconducting gap nodes in the ground state of UTe2. Our magnetic penetration depth measurements for three field orientations in three crystals all show the power-law temperature dependence with exponents close to 2, which excludes single-component spin-triplet states. The anisotropy of low-energy quasiparticle excitations indicates multiple point nodes near the ky- and kz-axes in momentum space. These results can be consistently explained by a chiral B3u + iAu non-unitary state, providing fundamentals of the topological properties in UTe2.