Angle resolved photoemission spectroscopy and X-ray diffraction study on IrTe1.6Se0.4

IrTe2 shows an interesting phase transition accompanying $\mathbf{q} = (1/5, 0, 1/5)$ lattice distortion, Ir valence fluctuation, and $J_{eff} = 1/2$ dimer formation. In order to study the role of anion doping, we investigated IrTe$_{1.6}$Se$_{0.4}$ which is known to exhibit $\mathbf{q} = (1/6, 0, 1/6)$ lattice distortion and higher transition temperature, about 370 K. The electronic structure of IrTe$_{1.6}$Se$_{0.4}$ single crystal was investigated by using angle resolved photoemission spectroscopy before and after the dimerization transition, which displays abrupt changes. Ir valence, investigated by corelevel X-ray photoemission, varies continuously from a pure Ir$^{3+}$ state to Ir$^{4+}$:Ir$^{3+} \simeq 1:1$ state, while x-ray diffraction measurement reveals a first order structure transition. In this talk, we will discuss an implication of our observations.