Nonexcitonic mechanism for electronic and structural phase transitions in Ta 2 Ni ( Se , S ) 5

The authors challenge a long-standing view of Ta₂NiSe₅ as an excitonic insulator by revealing a nonexcitonic origin for its phase transitions. Using systematic density functional theory calculations across the Ta₂Ni (Se, S) ₅ series, they show that structural distortions and charge doping account for the observed metal-insulator transitions. The calculations explain measured angle-resolved photoemission spectra with excellent accuracy, reconciling conflicting experimental observations and establishing a lattice-driven mechanism for the transitions in this system.