Taichi Okuda Hiroshima Synchrotron Radiation Center, Hiroshima University, 2-313 Kagamiyama Higashi-Hiroashima 739-0046, Japan
Topological insulators (TI) are the new class of quantum matter possessing topological surface state (TSS) in the bulk energy gap. This state demonstrates spin-polarized massless Dirac cone (DC) behavior with spin orientation of the TSS locked with the crystal momentum and resulting in a helical spin structure which offers the electrons protection against backscattering and has great appeal for spintronics applications.
For real applications, however, there are many hurdles to overcome. One is the realization of the high enough bulk resistivity that is necessary for emerging the property of TSS in the transport measurement. Even though the material has enough bulk energy band gap and possessing high bulk resistivity, the tuning of the Fermi level at the TSS is also necessary. To this end many efforts have been made to control the chemical potential of TIs by means of electron or hole doping by element substitutions. However, it is also reported that the small amount of gas adsorption causes the energy shift of TSS and casts away the efforts of carrier control.
Here I present some investigations of the ideal TIs by means of our recently developed high-resolution spin-ARPES (SARPES) machine named ESPRESSO[1]. Bi2Se2Te and Bi2Te2Se are predicted as new TIs possessing high bulk resistivity[2]. Our SARPES results of them show very high spin polarization at the TSS and suggest that the materials are one of the ideal TIs[3]. As the topic of controlling the chemical potential the new attempt of the Fermi surface tuning without introducing any foreign elements on TlBiSe2 will be also introduced[4]. Finally, as the example of the physically protected TSS from the external perturbation the bulk sensitive ARPES and SARPES results of Pb based ternary telluride PbBi4Te7 will be presented[5].
[1] T. Okuda et al., Rev. Sci. Instrum. 82, 103302 (2011).
[2] Z. Ren et al., Phys. Rev. B 82, 241306 (2010).
[3] K. Miyamoto et al., Phys. Rev. Lett. 109, 166802 (2012).
[4] K. Kuroda et al., arXiv:1308.5521(2013).
[5] Taichi Okuda et al., Phys. Rev. Lett. submitted.