Orbital contributions in the element-resolved valence electronic structure of Bi$_2$Se$_3$

In this work, we studied the bulk band structure of a topological insulator (TI) Bi2Se3 and determined the contributions of the Bi and Se orbital states to the valence bands using standing wave-excited hard x-ray photoemission spectroscopy (SW-HAXPES). This SW technique can provide the element-resolved information and extract individual Bi and Se contributions to the Bi2Se3 valence band. Comparisons with density functional theory (DFT) calculations (LDA and GW) reveal that the Bi 6s, Bi 6p, and Se 4p states are dominant in the Bi2Se3 HAXPES valence band. These findings pave a way for studying the element-resolved band structure and orbital contributions of this class of TIs.