Investigation and manipulation of spin polarized Dirac surface state in the chalcogenide topological insulators

A classification of material phases is a fundamental concept in condensed matter physics to clarify particular states of matter and usually it is specified with the spontaneous breaking symmetry. For examples, the ferromagnetic materials in which the magnetic moments form ordered state can be classified into the different material phase from non-magnetic one with the broken timereversal symmetry. Superconducting states also can feature an unique material phase regarding the broken gauge symmetry. In 1980s, the new concept to classify materials without the broken symmetry but ”topology” of the wave function in Hilbert space was discovered and intensively developed. Eventually, the concept leaded to the great discovery of ”topological insulator” in 2000s. The easiest way to clarify the new material phase is a particular insulator in which an existence of a metallic state is promised at the boundary (surface). Furthermore, one of the greatest feature of the topological insulator is that the metallic surface state behaves a spin-helical and massless Dirac fermion whose motion is governed by massless Dirac equation. In contrast to Graphene, the Dirac fermion in the topological insulator is described with the real spin instead of the pseudo-spin. As a consequence, the Dirac fermion in topological insulator can directly couple to the magnetic field, which can provide us with a fertile playground to study the intriguing relativistic physical phenomena as well as the realization of the high performance spintronic devices. This dissertation guides one to bring the novelties of topological insulators into the reality through the investigation and manipulate of the spin polarized Dirac surface state with spin-and angle-resolved photoemission spectroscopy (spin-ARPES) with synchrotron radiation and the material growths. In Chapter 4 of this thesis we study the precise electronic and magnetic structures at the surface of the prototypical topological insulator Bi2Se3 with non-magnetic and magnetic impurity doping investigated by high-resolution ARPES measurement. To further search an ideal topological insulator, the electronic structures of two candidates for the topological insulator, TlBiSe2 and PbBi2Te4, are studied and it is demonstrated that the both of the candidates are topological insulator in Chapter 5 of this thesis. Especially, it is revealed that TlBiSe2 possesses an ideal Dirac surface state which features in-gap Dirac point which has never been achieved in the other topological insulators. We 1 further discuss the spin textures of the Dirac surface state and the surface structure of TlBiSe2 in Chapter 6 and Chapter 7 of this thesis. Noteworthy, the reversal spin current regime can be realized with the methodology introduced in Chapter 6. These our finding can open path way to study intriguing physical phenomena and design the future devices on the surface. In Chapter 8 of this thesis, we come back to the surface state in the prototypical topological insulator Bi2Se3 and highlight the circular polarization dependence in ARPES and SARPES measurements, and develop a methodology for the spin manipulation in the spin polarized Dirac system that may facilitate further application of opt-spintronic devices.