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Momentum-dependent spin-polarized surface states in ultrathin Bi films
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Hirahara, Toru1; Miyamoto, Koji1; Matsuda, Iwao1; Kadono, Toshiharu1; Kimura, Akio1; Nagao, Tadaaki1; Bihlmayer, Gustav2; Chulkov, E. V.3; Qiao, S.1; Shimada, Kenya1; Namatame, Hirofumi1; Taniguchi, Masaki1; Hasegawa, Shuji1
1Japan;
2Germany;
3Spain |
Spintronics, which aims at the utilization of the spin degree of freedom in addition to the charge, has attracted wide interest due to their promising potentials in realizing new functionalities in devices. Spin manipulation is the key factor in spintronics, and the conventional style was to develop novel ferromagnetic materials. On the other hand, it was found that spin-spit two-dimensional electron gases can be formed in asymmetric quantum wells controlled by an electric field even for nonmagnetic materials. This is called the Rashba effect, due to the spin-orbit interaction and the structure inversion asymmetry (SIA) [1].
At the crystal surface, the same effect occurs due to the SIA in the surface-normal direction and spin-split surface states have been found for Au(111) [2]and W(110)-H [3] surfaces. Bi is a very heavy element and its electronic structure is highly influenced by the spin-orbit (SO) interaction. Due to this significant SO-coupling, surface states near the Fermi level on low-index Bi crystals were also said to show large spin-splitting from first-principles calculations [4]. However although some information about spin-dependent scattering has been obtained by scanning tunneling spectroscopy measurements [5], there has been no direct observation of the spin structure in a wide range of energy-momentum space. Therefore in the present study, we performed spin and angle resolved photoemission measurements on Bi(001) films to clarify the spin-polarization of the electronic structure. We succeeded in resolving the spin-up and down channels not only for the surface states at the Fermi level but also for those at the spin-orbit gap. The spin structure was antisymmetric with respect the Γ point and the in-plane spin polarization was as large as 0.5. Furthermore, we compared our k-dependence of the spin-polarization with ab initio calculations and obtained good consistency. The details will be discussed in the presentation.
[1] R. Winkler, "Spin-orbit coupling effects in two-dimensional electron and hole systems", (Springer-Verlag, 2003)
[2] M. Hoesch et al., PRB 69 241401
[3] M. Hochstrasser et al., PRL 89, 216802
[4] Yu. M. Koroteev et al., PRL 93 046403; T. Hirahara et al., PRL 97, 146803
[5] J. I. Pascual et al., PRL 93, 196802 |