Determination of the band parameters of bulk 2H-MX (M = Mo, W; X = S, Se) by angle-resolved photoemission spectroscopy.

Monolayer MX (M = Mo, W; X = S, Se) has recently been drawn much attention due to their application possibility as well as the novel valley physics. On the other hand, it is also important to understand the electronic structures of bulk MX for material applications since it is very challenging to grow large size uniform and sustainable monolayer MX. We performed angle-resolved photoemission spectroscopy and tight binding calculations to investigate the electronic structures of bulk 2H-MX. We could extract all the important electronic band parameters for bulk 2H-MX, including the band gap, direct band gap size at K (-K) point and spin splitting size. Upon comparing the parameters for bulk 2H-MX (our work) with mono- and multi-layer MX (published), we found that stacked layers, substrates for thin films, and carrier concentration significantly affect the parameters, especially the band gap size. The origin of such effect is discussed in terms of the screening effect.