Spin polarization of Dirac-cone surface state formed by 5d electrons

       Recently, we have discovered that the surface of W(110) shows a spin-polarized Dirac-cone state within a spin-orbit-induced gap, which is reminiscent of a TSS [1]. Here, in contrast to so-far studied topological insulators, the surface structure has C2v symmetry. The C2v symmetry strongly influences the dispersion of the Dirac-cone surface state, resulting in a flattened Dirac-cone. W(110) is suitable to research the spin feature of the photoelectrons dependent on the light polarization on material with C2v.


  We have studied the spin feature of Dirac-cone surface state at W(110), using SARPE spectroscopy with various light polarizations; left and right circular or s- and p- polarizations. We have noted that the observed spin feature of photoelectrons excited by p-polarized light is opposite to the case of s-polarized light for tangential spin component. According to dipole selection rule, we can observe the spin feature of even orbital symmetry and odd orbital symmetry by p-polarized light and s-polarized light, respectively. In that, their results show the orbital dependence of spin feature of the Dirac-cone-like surface state [2].


  On the other hand, in the case of circular polarized light, not only tangential spin component but also radial and out-of-plane spin component can be observed. The observed complex spin feature accepts strongly influenced by C2v symmetry. In detail, I introduce you in my presentation.


[1] K. Miyamoto et. al., Phys. Rev. Lett. 108, 066808 (2012).


[2] K. Miyamoto et al. Phys. Rev. B 93, 161403(R) (2016).