Raman evidence for high-temperature 2a × 2a charge density wave in disorder-W-intercalated NbSe₂

Correlated electron systems provide platforms for macroscopic quantum phenomena. We investigate lattice dynamics and ultrafast carrier relaxation in disorder-W-intercalated NbSe₂ using temperature-dependent Raman spectroscopy and transient absorption microscopy (TAM). Intercalation induces a 2a × 2a superstructure accompanied by a localized vibrational mode of W atoms (~108 cm^-1) and a zone-folded phonon mode from M point (~156 cm^-1). Anharmonicity and thermal melting of the zone-folded mode provide evidence for that the 2a × 2a superstructure relates to a high-temperature charge density wave (CDW), attributed to selectively enhanced electron-phonon coupling (EPC). Conversely, the two-phonon soft mode exhibits unusual temperature dependence, indicating the 3a × 3a CDW transition temperature decreases from 35.6 K to 11.8 K. TAM results corroborate this suppression, as prolonged fast and slow relaxation time constants reflect structural disorder and charge redistribution. Our findings demonstrate charge transfer induced by disordered intercalation selectively modulates EPC, offering insights into tailoring quantum orders in correlated materials.