Superstructure and its domain structure in layered IrTe$_2$ at low temperatures

IrTe$_2$, forming in layered CdI$_2$ structure, exhibits a unique phase transition accompanied by the appearance of diamagnetism and a sharp increase of electrical resistivity. This transition has been discussed to be due to a charge-density-wave formation related to the Fermi surface nesting [1]. In this talk, we will report the three dimensional superstructure below the transition temperature, obtained from electron diffraction patterns using low-temperature transmission electron microscopy. The superstructure is characterized by the presence of the superlattice reflections with the modulation wave vector q$=$ 1/5 [101]. Its domain structure and chemical doping effects on the modulation wave vector will also be discussed.\\[4pt] [1] J. J. Yang et al., PRL 108, 116402 (2012).