Atomic scale visualization of light-induced phase transition in candidate excitonic insulator Ta₂NiSe₅

Ta₂NiSe₅ has been proposed as a strong candidate for realizing the excitonic insulator phase. The temperature dependent gap opening and characteristic flat band top at the Gamma point have been suggested as evidence of this exotic phase of matter. However, orthorhombic to monoclinic structural phase transition occurring at the same transition temperature makes it confusing to tell if the insulating low temperature phase is driven by an electronic order or structural order. To address this question, in this talk, we will discuss the manipulation of the low temperature insulating phase of the Ta₂NiSe₅ with burst shots of high fluence optical pulses followed by STM investigation. Topographic study reveals the local structural phase and spectroscopic study reveals the local electronic phase of the light-induced state. By mapping possible photoexcited changes in structural and electronic phases and examining their spatial correlation, we aim to provide a hint for the origin of the candidate excitonic insulating phase in Ta₂NiSe₅.