Harnessing Van Hove singularities for terahertz photoresponse via Fermi surface reconstruction in kagome lattices.

The trihexagonal tiling system exhibits strong electron-electron interactions, positioning it as a key condensed matter platform for studying geometrically frustrated lattices made up of corner-sharing triangles. Its phase-transition-driven lattice modulations enable Fermi surface reconstruction, while emergent van Hove singularities near the Fermi level and correlated band anomalies present critical challenges in understanding electronic interaction mechanisms. By combining temperature-dependent spectroscopy, angle-resolved photoemission, and density functional theory calculations, we demonstrate a 61-fold enhancement in terahertz direct detection mode, ultra-low noise (1.38 × 10⁻²⁵ A²/Hz) below phase transition temperature, and broadband operation up to 100 GHz in beat-note heterodyne mode. These results are directly correlated with the Fermi surface reconstruction induced by phase transitions. This work positions geometrically frustrated lattices as a powerful platform for studying correlated quantum phenomena, offering new pathways for the design of advanced quantum devices.