Present and future trends in spin ARPES

Spin-orbit (SO) coupling combined with space inversion symmetry breaking is at the origin of the lifting of the spin degeneracy in the band structure of many materials. The momentum-dependent energy splitting and the degree of spin polarization are indicative of the strength and symmetry of the SO interaction, and enter in the figure of merit of essentially all conceptual designs aiming to control the electron spin degree of freedom in solids. Here we briefly review the role played by spin-and-angle-resolved photoemission (spin ARPES or SARPES) in revealing the spin polarization specifically in the topological states of 3-dimensional (3D) topo- logical insulators (TIs), and we discuss how the progress in the technique can assist the rise of several active fields like spintronics, spin-orbitronics or the generation of spin-polarized beams.