  Nearly localized moire flat bands in momentum space, arising at particular
twist angles, are the key to achieve correlated effects in transition-metal
dichalcogenides. Here, we use angle-resolved photoemission spectroscopy (ARPES)
to visualize the presence of a flat band near the Fermi level of van der Waals
(vdW) WSe2/MoSe2 heterobilayer grown by molecular beam epitaxy. This flat band
is localized near the K point of the Brillouin zone and has a width of several
hundred meVs. By combining ARPES measurements with density functional theory
(DFT) calculations, we confirm the coexistence of different domains, namely the
reference 2H stacking without layer misorientation and regions with arbitrary
twist angles. For the 2H-stacked heterobilayer, our ARPES results show strong
interlayer hybridization effects, further confirmed by complementary micro-
Raman spectroscopy measurements. The spin-splitting of the valence band at K is
determined to be 470 meV. The valence band maximum (VBM) position of the
heterobilayer is located at the Gamma point. The energy difference between the
VBM at Gamma and the K point is of -60 meV, which is a stark difference
compared to individual 1L WSe2 and 1L WSe2, showing both a VBM at K.
