Synthesis and Characterization of New Topological Insulators

In this talk, I will show detailed information on synthesizing process and characterization results of new topological insulator (TI) materials with interesting properties. Among the synthesized materials, TlBiSe$_2$ was the first ternary TI and has the largest bulk band gap [1], TlBi(S$_{1-x}$,Se$_x$)$_2$ presents a topological phase transition with unexpected Dirac mass [2], BiTe$_2$Se presents a large bulk resistivity [3], and Bi$_{1.5}$Sb$_{0.5}$Te$_{1.7}$Se$_{1.3}$ has finally achieved the surface-dominated transport in bulk single crystals [4]. It is essentially easy to grow single crystals of all the chalcogenides above, because those compounds melt congruently at relatively low temperatures. Therefore, the melt-growth method is applicable if the raw materials are in a sealed condition, e.g., in a quartz tube. However, crucial techniques for obtaining high-quality samples vary between the systems. Besides the growth method, characterizations of the transport properties, ARPES, the X-ray diffraction, and quantitative chemical analysis will also be presented. \\[4pt] This work is in collaboration with A. A. Taskin, S. Sasaki, Zhi Ren, K. Eto, T. Minami, and Y. Ando (Osaka Univ.), and T. Sato, S. Souma, H. Guo, K. Sugawara, K. Kosaka and K. Nakayama, and T. Takahashi (Tohoku Univ.). \\[4pt] \noindent [1] T. Sato, Kouji Segawa, T. Takahashi, Y. Ando {\it et al.}, Phys. Rev. Lett. {\bf 105}, 136802 (2010). \\ \noindent [2] T. Sato, Kouji Segawa, Y. Ando, T. Takahashi {\it et al.}, Nature Physics, {\bf 7}, 840 (2011). \\ \noindent [3] Zhi Ren, Kouji Segawa, Y. Ando {\it et al.}, Phys. Rev. B (Rapid Comm.) {\bf 82}, 241306(R) (2010). \\ \noindent [4] A. A. Taskin, Kouji Segawa, and Y. Ando {\it et al.}, Phys. Rev. Lett. {\bf 107}, 016801 (2011).