Photo-induced semimetallic states realised in electron–hole coupled insulators

• DOI: 10.1038/s41467-018-06801-1
• Publication Date: 2018-10-11T15:26:24Z
• Authors: Kozo Okazaki; Yu Ogawa; Takeshi Suzuki; Takashi Yamamoto; Takashi Someya; Shoya Michimae; Mari Watanabe; Yangfan Lu; Minoru Nohara; Hidenori Takagi; Naoyuki Katayama; Hiroshi Sawa; Masami Fujisawa; Teruto Kanai; Nobuhisa Ishii; Jiro Itatani; Takashi Mizokawa; Shik Shin
• Keywords: Superconductivity (cond-mat.supr-con); Condensed Matter - Materials Science; Condensed Matter - Strongly Correlated Electrons; Strongly Correlated Electrons (cond-mat.str-el); Science; Condensed Matter - Superconductivity; Q; Materials Science (cond-mat.mtrl-sci); FOS: Physical sciences; 7. Clean energy; Article

AbstractUsing 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 realisation 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.