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Séminaire spécial MCBT

Mercredi 18 décembre 2013 à 10h00,
Salle Remy Lemaire, K223

Orateur : Kazuyuki Sakamoto (Chiba University, Japan)
"Peculiar spin-polarized electronic states on semiconductor surfaces"


Generally, the electronic states of opposite spin orientation are considered to be degenerate in nonmagnetic materials due to the presence of both time-reversal symmetry and space-inversion symmetry. In a 2D system such as a crystal surface, the latter symmetry is broken and the degeneracy is lifted by spin-orbit coupling. This effect, which is called the Rashba-Bychkov (RB) effect [1], is a novel exotic low-dimensional solid-state property that produces spin-polarized electronic states even for nonmagnetic materials, and is the key factor for operating a spin field-effect transistor [2] that is one of the most prominent semiconductor spintronics devices. In this talk, I first present peculiar RB effects that originate from the symmetry of the surface, such as the abrupt change of the spin polarization vector to a direction that is not possible to point with normal RB effect [3], and the presence of peculiar vortical RB splitting at a point without time-reversal invariance, which was believed to be a critical condition for RB effect [4]. Then, I show results on RB systems with peculiar spin structures, in which the backscattering of electron spin with a non-magnetic impurity are considerably suppressed [5], and also discuss the origin of these spin structures based on a combination of the RB effect and the valley degree of freedom [6]. All these novel quantum phenomena are corroborated by the combination of high-resolution photoemission and spin-resolved photoemission measurements, scanning tunneling microscopy, and a state-of-the-art theoretical calculation.

[1] Y.A. Bychkov & E.I. Rashba, JETP Lett. 39, 78 (1984).
[2] S. Datta & B. Das, APL 56, 665 (1990).
[3] K. Sakamoto et al., PRL 102, 096805 (2009).
[4] K. Sakamoto et al., PRL 103, 156801 (2009).
[5] K. Sakamoto et al., Nature Comm. 4, 2073 (2013).
[6] S. Goswami et al., Nature Phys. 3, 41 (2007).

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