Discovery of Room-Temperature Charge Order in a Correlated Kagome Superconductor LaRu₃Si₂

The kagome lattice is an intriguing and rich platform for discovering, tuning and understanding the diverse phases of quantum matter. The possibility to access correlated order at room temperature has been extensively studied, but has remained elusive. Here we utilize single crystal X-ray diffraction to discover charge order beyond room-temperature in the prototypical kagome superconductor La(Ru_1-xFe_x)₃Si₂ (x = 0, 0.01, 0.05) [1]. Namely, it is found that charge order related to out-of-plane displacements of Ru atoms appears below T_CO-I = 400 K. The appearance of a second charge ordered phase, competing with the primary one, is found at lower temperatures T_CO-II = 80-170 K. Furthermore, first principles calculations show that in LaRu₃Si₂, both the kagome flat band and the van Hove point with strong electron-electron interaction, formed by the Ru-dz² orbitals, are very close to the Fermi energy. Our results present the first example of a charge ordered state at or above room temperature in the correlated kagome lattice and classifies the system LaRu₃Si₂ as the superconductor with the highest charge ordering temperature. Our finding introduces a new platform for the exploration of the correlation-driven room temperature phases (e.g., superconductivity, collosal magnetoresistance, etc.) in layered quantum materials, and also promotes the practical development of charge-order-related technology and devices.

[1] I. Plokhikh, C. Mielke III et al. arXiv:2309.09255 (2023).