Anisotropic effective hole masses. ARPES cut data along the in-plane momentum defined by the angle θ (see Fig. 2(a) for definition) for (a) ReS2 and (b) ReSe2. All the data sets are centered around the Z-point at which VBM is located. The dotted lines indicate a quadratic function fitting the dispersions of the top-most bands. The effective mass from the quadratic fit function for each angle can be extracted and is plotted for ReS2 and ReSe2 in (c). Arrows indicate crystallographic orientation of ReX2.