Phys. Rev. B 93, 161403(R) (2016).
The surface of W(110) exhibits a spin-orbit-induced Dirac-cone-like surface state, which is of mainly dz2 orbital character near Γ, although it is strongly influenced by the twofold C2v surface symmetry. Its distinctive k-dependent spin polarization along ΓH is revealed by spin- and angle-resolved photoemission excited with p and s-polarized light. The spin texture of the surface state is found to change sign upon switching from p- to s-polarized light. Based on electronic-structure calculations, this behavior is explained by the orbital composition of the Dirac-cone-like state. The dominant part of the state has even mirror symmetry and is excited by ppolarized light. A minor part with odd symmetry is excited by s-polarized light and exhibits a reversed spin polarization. Our study demonstrates in which way spin-orbit interaction combines the spin degree of freedom with the orbital degree of freedom and opens a way to manipulate the spin information gathered from the Dirac-cone-like surface state by light. Our results prove that “spin control” is not restricted to topological surface states with p-type orbital symmetry in topological insulators.
Phys. Rev. B 93, 085412 (2016).
The spin texture of the unoccupied surface electronic structure of the metal-semiconductor hybrid system Tl/Ge(111)−(1×1) is investigated by spin- and angle-resolved inverse photoemission as well as quasiparticle band-structure calculations. Spin-polarized surface bands with rotating spin and giant energy splitting are found along ΓK(K′), forming valleys with alternating out-of-plane spin polarization at K and K′. This behavior is known from the equivalent hybrid system on Si(111). Along ΓM, a pair of surface bands appears within a projected bulk band gap, whose equivalent on Tl/Si(111) is a surface resonance because, there, it overlaps with bulk states. Surprisingly, the spin splitting of these bands on Tl/Ge(111) is much smaller than on Tl/Si(111) despite the stronger surface localization and the heavier substrate. Our detailed analysis of the band structure and a tight-binding model including all relevant interactions show that a remarkable interplay between spin-orbit coupling and hybridization is responsible for this unexpected result. The comparison between the two similar hybrid systems demonstrates that the strength of the spin-orbit coupling alone, based on the atomic number of the respective elements, is not sufficient to estimate spin splittings of spin-orbit-influenced surface states.