Non-Coulomb strong electron-hole binding in Ta2NiSe5 revealed by time- and angle-resolved photoemission spectroscopy
Abstract
We reveal an ultrafast purely electronic phase transition in , which is a plausible excitonic insulator, after excited by an ultrafast infrared laser pulse. Specifically, the order parameter of the strong electron-hole binding shrinks with enhancing the pump pulse, and above a critical pump fluence, a photo-excited semimetallic state is experimentally identified with the absence of ultrafast structural transition. In addition, the bare valence and conduction bands and also the effective exciton binding energy in ~are determined. These findings and detailed analysis suggest a bare nonequilibrium semimetallic phase in Ta2NiSe5 and the strong electron-hole binding cannot be exclusively driven by Coulomb interaction.
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