Physical Properties of New U-based Kagome and 2-D Van der Waals Compounds

The electronic band structure of hexagonal Kagome materials is predicted to contain coexisting flat bands, van Hove singularities, and Dirac points. Materials in the hexagonal RM₆X₆ (166) family (R=rare-earth, M=transition metal, X=Ge, Sn) contain Kagome nets of transition metal ions and are of particular interest because their chemical tunability enables access to these interesting band structure features and to novel ground states. We successfully synthesized single crystals of UV₆Sn₆, UNb₆Sn₆, and UCr₆Ge₆ [1-3]. We found a complex magnetic field-temperature phase diagram and two zero-field magnetic transitions at T_N=29 K, T₂=24 K for UV₆Sn₆ and T_N=46 K, T₂=42 K for UNb₆Sn₆. UCr₆Ge₆ has an enhanced electronic specific heat coefficient (~90 mJ/mol-K²), possibly due to the Cr Kagome flatbands near the Fermi level.

2-D Van der Waals (VdW) materials provide the means to explore strong electronic correlations, quantum criticality, and magnetism in the 2-D limit. We recently synthesized single crystals of the 2-D VdW material β-UTe₃ [4], which crystallizes in the orthorhombic Cmcm structure. Here, we find 3-D bulk ferromagnetism at T_C~13 K. Neutron diffraction indicates the presence of 3-D magnetic order and 2-D fluctuations, similar to the 2-D var der Waals magnet CrSBr. We find that the Curie temperature of β-UTe₃ is enhanced up to T_C=35 K in the 2-D limit through exfoliation.

[1] S.M. Thomas et al. Nat. Quant. Mater. 10, 66 (2025); [2] Z. W. Riedel et al. Phys. Rev. Mater. 9, 084401 (2025); [3] Z. W. Riedel et al. (unpublished); [4] S. M. Thomas et al. arXiv:2506.15667