Unveiling Strong Electron Correlations and Charge Density Wave Instability in NbTe2 Induced by Sn Incorporation

The interplay between charge density waves (CDWs) and electron correlations in transition metal dichalcogenides (TMDs) remains a subject of intense debate. NbTe2 is a unique member of this family, exhibiting a significant structural distortion and a high-temperature CDW transition (∼550 K). However, this comparably high transition temperature has obscured the direct spectroscopic observation of the electronic structure evolution across the phase boundary since long, hindering a microscopic understanding on the CDW mechanism. Here, we have successfully overcome this limitation by synthesizing Sn0.01NbTe2 single crystals, which effectively suppress the CDW transition temperature to 254 K. This suppression allows us to utilize angle-resolved photoemission spectroscopy (ARPES) to directly visualize the momentum-space band structure reconstruction accompanying the suppressed phase transition, which is identified by transport measurements and is consistent with the known 3 × 1 structural distortion of the NbTe2 system. Crucially, by comparing our ARPES data with first-principles calculations that account for effects of Sn incorporation, we identify a chemical potential shift induced by the incorporation. This subtle electronic tuning, accompanied by incorporation, effectively modifies the Fermi surface topology and suppresses the CDW transition temperature from ∼550 to 254 K. This shift moves the Fermi level into the high density of states (DOS) region of the monoclinic phase, thereby disrupting the energy-saving conditions of the distorted lattice and explaining the suppression of the transition temperature. Our findings provide evidence for substantial deviations from the DFT description of the electronic structure, while the microscopic origin of these deviations remains to be determined.