Three-dimensional bulk band dispersion in polar BiTeI with giant Rashba-type spin splitting

In layered polar semiconductor BiTeI, giant Rashba-type spin-split band dispersions show up due to the crystal structure asymmetry and the strong spin-orbit interaction. Here we investigate the three-dimensional (3D) bulk band structures of BiTeI using the bulk-sensitive hν-dependent soft x-ray angle-resolved photoemission spectroscopy (SX-ARPES). The obtained band structure is shown to be well reproducible by the first-principles calculations, with huge spin splittings of ~300 meV at the conduction-band minimum and valence-band maximum located in the kz=π/c plane. It provides direct experimental evidence of the 3D Rashba-type spin splitting in a bulk compound.