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Jeudi 16 Mai 2013, 14h
Amphi Holweck, Esc C, 1ème etage
Rashba spin-orbit interactions at surfaces
Stephane Pons
Institut des NanoSciences de Paris (INSP)
In non-magnetic solids spin degeneracy of the electronic bands is a
consequence of time reversal symmetry and inversion symmetry. However when inversion symmetry is broken, the degeneracy can be lifted by spin-orbit interactions. This interaction introduces a momentum-dependent effective magnetic field which separates the spin density of states in the reciprocal space. At surfaces, where translation symmetry is broken, this phenomenon is known as Rashba effect. The Rashba splitting was first evidenced in an ARPES study of the Shockley surface states of gold. It is also known to be at the origin of the peculiar properties of recently discovered topological
insulator.
On some peculiar materials the spin splitting is more than 10 times larger than expected by the Rashba effect [eg. 1-3]. This effect was called “giant Rashba splitting”. The origin of the giant spin orbit interaction at
surfaces is still under debate. In my talk, I will make a short review of the results obtained for giant Rashba systems and introduce the possible phenomena at the origin of the enhancement of the band splitting. I will show that a giant Rashba splitting can be induced in a single layer of metal atoms at the surface of a semiconductor sample [2-3]. This phenomenon couldbe of great interest for studying the effect of strong spin-orbit
interactions on superconductivity in the recently discovered ultrathin
superconductors [4-5]. The interplay of superconductivity and Rashba
spin-orbit interaction is one of the projects which will be addressed with Nanospecs ARPES platform developed at LPEM.
[1] E. Frantzeskakis et al. Tunable spin gaps in a quantum-confined
geometry. Phys. Rev. Let., 101, 196805 (2008).
[2] I. Gierz et al. Silicon Surface with Giant Spin Splitting. Phys. Rev.
Let. 103, 046803 (2009).
[3] E. Frantzeskakis, S.Pons, and M. Grioni. Band structure scenario for the
giant spin-orbit splitting observed at the Bi/Si(111) interface. Phys. Rev.
B 82, 085440 (2010).
[4] T. Zhang et al. Superconductivity in one-atomic-layer metal films grown
on Si(111). Nat. Phys. 6, 104 (2010).
[5] C. Brun et al. The effect of disorder on extreme two-dimensional
superconductivitors. submitted.