Extended Data Figure 2: Raw spectra and second derivatives of 1UC, 1.7UC, 2UC and 30UC films.

a, f, k, p, Plots of the raw spectrum at Γ, the second derivative at Γ, the raw spectrum at M, and the second derivative at M for the 1UC film, respectively, taken at 10 K. b, g, l, q, The same plots for the 1.7UC film taken at 13 K. c, h, m, r, The same plots for the 2UC film taken at 15 K. d, i, n, s, The same plots for the 30UC film taken at 50 K. e, j, o, t, The same plots for the 30UC film taken at 140 K. Data for the 30UC film are symmetrized about the high-symmetry points (indicated by the green line), and were taken with 25-eV photons. We observe a band splitting in the 30UC film at M, at low temperature (s). This band splitting closes at higher temperature (140 K), where we now observe only one band (t).