image: Fig. 1. There are two different conduction band minima (CBMs) arise at the X point (valley degeneracy NvX=3) in the Brillouin zone, one dominated by the d-orbital of X atoms (minimum at ...

Using optical excitation to create non-moving excitons—that is, excitons located at the minimum and maximum of the conduction band and valence band, respectively—is standard in insulators.