Discovery of high-temperature charge order and time-reversal symmetry-breaking in the kagome superconductor YRu3Si2

Identifying high-temperature unconventional charge order and superconductivity in kagome systems is crucial for understanding frustrated, correlated electrons and enabling future quantum technologies. Here, we report that the kagome superconductor YRu3Si2 hosts an exceptional interplay of charge order, magnetism, and superconductivity, revealed through a comprehensive suite of muon spin rotation (μSR), magnetotransport, X-ray diffraction, and density functional theory (DFT). We identify a high-temperature charge-ordered state with propagation vector (1/2,0,0) and a record onset temperature of 800 K, unprecedented in kagome systems and quantum materials more broadly. μSR measurements further reveal time-reversal symmetry-breaking below 25 K and field-induced magnetism near 90 K, features mirrored in the magnetoresistance, which reaches 45% at low temperatures. Band-structure calculations show two van Hove singularities near the Fermi level, including one within a flat band. At low temperatures, YRu3Si2 becomes superconducting below Tc = 3.4 K with either two full isotropic gaps or an anisotropic nodeless gap. These results establish YRu3Si2 as a prime platform for studying correlated kagome physics. The authors report the discovery of charge order with onset temperature of 800 K in the kagome superconductor YRu3Si2. In addition, they observe time-reversal symmetry breaking below 25 K, field-induced magnetism below 90 K and bulk multi-gap superconductivity below 3.4 K.