Photoinduced Phase Transition From Excitonic Insulator To Semimetal-Like State In Ta2n1-Xcoxse5 (X=0.10)

We report time-resolved angle-resolved photoemission study on Ta2Ni1-xCoxSe5 (x = 0.10) in which the excitonic insulator (EI) transition temperature is reduced by Co substitution for Ni. In the photoinduced phase, the conduction band is clearly observed and the energy gap between the conduction and valence bands is undetectably small within the energy resolution. Assuming that the energy gap is closed, the conduction band crosses or overlaps with the valence band near the Fermi level resembling a nodal semimetal.