title: Ultrafast electron dynamics at the Dirac node of the topological insulator Sb2Te3.
abstract: Topological insulators (TIs) are a new quantum state of matter. Their surfaces and interfaces act as a topological boundary to generate massless Dirac fermions with spin-helical textures. Investigation of fermion dynamics near the Dirac point (DP) is crucial for the future development of spintronic devices incorporating topological insulators. However, research so far has been unsatisfactory because of a substantial overlap with the bulk valence band and a lack of a completely unoccupied DP. Here, we explore the surface Dirac fermion dynamics in the TI Sb2Te3 by time- and angle-resolved photoemission spectroscopy (TrARPES). Sb2Te3 has an in-gap DP located completely above the Fermi energy (EF). The excited electrons in the upper Dirac cone stay longer than those below the DP to form an inverted population. This was attributed to a reduced density of states (DOS) near the DP.
authors: Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
authors: Siyuan
authors: S
authors: Zhu
authors: Institute for Solid State Physics, the University of Tokyo, 5-1-5, Kashiwa-no-ha, Chiba 277-8581, Japan.
authors: Yukiaki
authors: Y
authors: Ishida
authors: Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
authors: Kenta
authors: K
authors: Kuroda
authors: Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
authors: Kazuki
authors: K
authors: Sumida
authors: State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Chang Ning Road, Shanghai 200050, China.
authors: Mao
authors: M
authors: Ye
authors: School of physical science and technology, Shanghai Tech University, 319 Yueyang Road, Shanghai 200031, China.
authors: Jiajia
authors: J
authors: Wang
authors: Department of Physics, State Key Laboratory of Surface Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China.
authors: Hong
authors: H
authors: Pan
authors: Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
authors: Masaki
authors: M
authors: Taniguchi
authors: State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Chang Ning Road, Shanghai 200050, China.|School of physical science and technology, Shanghai Tech University, 319 Yueyang Road, Shanghai 200031, China.
authors: Shan
authors: S
authors: Qiao
authors: Institute for Solid State Physics, the University of Tokyo, 5-1-5, Kashiwa-no-ha, Chiba 277-8581, Japan.
authors: Shik
authors: S
authors: Shin
authors: Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526, Japan.
authors: Akio
authors: A
authors: Kimura