Observation of a commensurate super modulation consistent with an intertwined charge density wave and antiferromagnetic phase in monolayer 1T-NbSe2

Monolayer 1T-phase NbSe 2 , a strongly correlated insulator hosting a frustrated spin lattice, has emerged as a promising platform for realizing exotic quantum phases arising from competing orders. Its insulating behavior originates from a charge-density-wave (CDW) state with Star-of-David (SD) clusters, each hosting a localized magnetic moment that forms a triangular spin network. Using scanning tunneling microscopy and spectroscopy (STM/STS), we report the observation of a long-wavelength supermodulation that is commensurate with the SD CDW. To explain this data, we construct a Landau free energy model, which reveals a symmetry-allowed coupling between the spin and charge degrees of freedom. Combined with density functional theory (DFT) calculations, we propose a plausible explanation for the modulation in terms of a phase in which the CDW order is entangled with a noncollinear antiferromagnetic (AFM) state. These findings provide new insights into the complex interplay of electronic correlation, magnetism, and lattice order in two-dimensional quantum materials.