Non-Coulomb strong electron-hole binding in Ta 2 NiSe 5 revealed by time- and angle-resolved photoemission spectroscopy

作者：Tian-wei Tang, Hongyuan Wang, Shaofeng Duan, Yuanyuan Yang, Chaozhi Huang, Yanfeng Guo, Dong Qian, Wentao Zhang · 发表于：Physical review. B./Physical review. B · 年份：2020 · DOI：10.1103/physrevb.101.235148 · 被引用次数：60 · 研究领域：2D Materials and Applications、Topological Materials and Phenomena、Perovskite Materials and Applications

We reveal an ultrafast purely electronic phase transition in ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$, 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 photoexcited semimetallic state is experimentally identified with the absence of ultrafast structural transition. In addition, the bare valence and conduction bands and also the effective masses in ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$ are determined. These findings and detailed analysis suggest a bare nonequilibrium semimetallic phase in ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$ and the strong electron-hole binding cannot be exclusively driven by Coulomb interaction.