Discovery of High-Temperature Charge Order and Magnetism in the Kagome Superconductor YRu₃Si₂

The identification of high-temperature unconventional charge order and superconductivity in kagome quantum materials is pivotal for deepening our understanding of geometrically frustrated and correlated electron systems, and for harnessing their exotic properties in future quantum technologies. In this talk, I will present a remarkably rich phase diagram [1] in the kagome superconductor YRu₃Si₂, uncovered through a unique combination of muon spin rotation (μSR), magnetotransport, X-ray diffraction (XRD), and density functional theory (DFT) calculations. Our study reveals the emergence of a charge-ordered state with a propagation vector of (1/2, 0, 0), setting a record onset temperature of 800 K for such an order in a kagome system and for quantum materials more broadly. In addition, we observe a pronounced enhancement of the internal field distribution sensed by the muon ensemble below 25 K, along with field-induced relaxation emerging below 90 K, indicating the presence of a hidden magnetic state. These transitions are mirrored in the magnetoresistance data, which show a clear onset at 25 K and a pronounced increase below 90 K, ultimately reaching a maximum magnetoresistance of 45%. Band structure calculations identify two van Hove singularities (VHSs) near the Fermi level, one of which resides within a flat band, suggesting a strong interplay between electronic correlations and emergent orders. At low temperatures, we find bulk superconductivity below T_c = 3.4 K, characterized by a pairing symmetry with either two isotropic full gaps or an anisotropic nodeless gap. Together, our findings point to a coexistence of high-temperature charge order, tunable magnetism, and multigap superconductivity in YRu₃Si₂, positioning it as a compelling platform for exploring strongly correlated kagome physics.

[1] P. Kral, et. al., and Z. Guguchia, arXiv:2507.06885 (2025).