Invited Paper TF-MoE8
Investigation of Peculiar Spin Electronic States Induced by Spin-Orbit Interaction Using High-Resolution Spin-Resolved Photoemission

Monday, December 8, 2014, 8:00 pm, Room Makai

Spin-orbit-interaction induced spin polarized surface states such as Rashba spin split states or topological surface states(TSS) are the new class of quantum mutter and getting much attention as the key materials for the realization of spintronic devices. Spin polarization reversal in the surface state bands with respect to time reversal symmetry point in these materials expects to suppress backscattering by nonmagnetic impurities and to realize dissipationless spin transport.

In case of Rashba systems, however, the possible back scattering to the spin split pair band having opposite spin polarization hampers the complete suppression of backscattering. In addition, some quasi particle interference pattern of STM measurements show the existence of the scattering path even in the topological insulators. Furthermore, for the real application one should also consider to protect the surface states from the contamination. It has been reported that small amount of gas adsorption can produce the band bending in the topological insulators and changes the property of the TSS dramatically. Thus, in order to use the spin-polarized surface states and realize the spintronic devices one should eliminate these problems.

Here I present some recent results of spin- and angle-resolved photoelectron spectroscopy (SARPES) that show the hints to solve these problems. The first example is a Rashba system on one-dimensional surface states. High-resolution SARPES of Au induced chain structure on vicinal Si(111) surface shows clearly one-dimensional Rashba spin-split states. Interestingly the spin polarization vector is not in-plane but points perpendicular to the surface deviating from the normal Rashba spin-split states. This out-of-plane spin polarization and the one-dimensional band structure will help to reduce the scattering probability of the electron in the system.

Bi film on vicinal Si(111) surface also shows interesting spin structure having out-of-plane spin polarization. Unlike the Bi film on normal Si(111) surface that has (111) orientation, the film on the Si(557) surface shows LEED pattern and surface band structures similar to those of Bi(110) surface. Because of the lower symmetry (C_1h) of the sample structure not only in-plane but also significant out-of-plane spin polarization has been observed.

As the other examples, the investigation of lead based topological insulator PbBi₄Te₇ will be presented. Surface and bulk sensitive SARPES measurement proved the existence of spin-polarized topological surface states protected physically under the quintuple layer. This protected TSS will open the pathway to utilize the spin-split electrons in the future.