Electronic structure, spin--orbit coupling, and interlayer interaction in bulk MoS$_2$ and WS$_2$

Transition metal dichalcogenides (TMDs) (MX$_2$ where M = Mo or W and X = S, Se, or Te) are theorized to possess unique spin-split valence bands along with rare spin--valley coupling, making them attractive for applications within the growing fields of spintronics and valleytronics. Despite the importance of the split valence band that governs the unique spin- and valley-physics of TMDs, there remain many questions regarding its origin and properties in bulk TMDs. In this talk, I will present high-resolution angle-resolved photoemission spectroscopy (ARPES) measurements of the electronic band structure of bulk TMDs MoS$_2$ and WS$_2$. Detailed comparison with first principle calculations will be shown. The role of the valence band splitting and how it can be controlled will be discussed.