Using light to manipulate materials into desired states is one of the goals in condensed matter physics, since light control can provide ultrafast and environmentally-friendly photonics devices. However, it is generally difficult to realise a photo-induced phase which is not merely a higher entropy phase corresponding to a high-temperature phase at equilibrium. Here, we report realization of photo-induced insulator-to-metal transitions in Ta2Ni(Se1-xSx)5 including the excitonic insulator phase using time- and angle-resolved photoemission spectroscopy. From the dynamic properties of the system, we determine that screening of excitonic correlations plays a key role in the timescale of the transition to the metallic phase, which supports the existence of an excitonic-insulator phase at equilibrium. The non-equilibrium metallic state observed unexpectedly in the direct-gap excitonic insulator opens up a new avenue to optical band engineering in electron-hole coupled systems.
@article{arxiv.1809.03166,
title = {Photo-induced semimetallic states realised in electron-hole coupled insulators},
author = {Kozo Okazaki and Yu Ogawa and Takeshi Suzuki and Takashi Yamamoto and Takashi Someya and Shoya Michimae and Mari Watanabe and Yangfan Lu and Minoru Nohara and Hidenori Takagi and Naoyuki Katayama and Hiroshi Sawa and Masami Fujisawa and Teruto Kanai and Nobuhisa Ishii and Jiro Itatani and Takashi Mizokawa and Shik Shin},
journal= {arXiv preprint arXiv:1809.03166},
year = {2018}
}