Role of spin-orbit coupling for the band splitting inα-Sb andα-Bi on SiC(0001).

Monolayer atomic thin films of group-V elements have a high potential for application in spintronics and valleytronics because of their unique crystal structure and strong spin-orbit coupling. We fabricated Sb and Bi monolayers on a SiC(0001) substrate by the molecular-beam-epitaxy method and studied the electronic structure by angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. The fabricated Sb film shows the (√3 × √3)R30° superstructure associated with the formation ofα-Sb, and exhibits a semiconducting nature with a band gap of more than 1.8 eV. Spin-resolved ARPES measurements of isostructuralα-Bi revealed the in-plane spin polarization for the topmost valence band, demonstrating its Rashba-splitting nature due to the space-inversion-symmetry breaking. We discuss the origin of observed characteristic band structure and its similarity and difference between Sb and Bi.