Imaging the coherent propagation of collective modes in the excitonic insulator Ta ₂ NiSe ₅ at room temperature

Excitonic insulators host a condensate of electron-hole pairs at equilibrium, giving rise to collective many-body effects. Although several materials have emerged as excitonic insulator candidates, evidence of long-range coherence is lacking and the origin of the ordered phase in these systems remains controversial. Here, using ultrafast pump-probe microscopy, we investigate the possible excitonic insulator Ta_2iSe_5 Below 328 K, we...