a, b, Transition from strong coupling to weak coupling, measured from the temperature dependence of Ω1 (red open circles) and (γc + γX1)/2 (purple triangles) (a) and Ω2 (red open circles) and (γc + γX2)/2 (purple triangles) (b). γc = 2.7 meV is constant with temperature. Ω1 and Ω2 drop below the average linewidth at about 100 K, showing the transition to the weak-coupling regime. Ω1 and Ω2 are extracted by fitting the angle-resolved white-light reflection spectra with equation (1) and the error bars correspond to the 95% confidence interval. γX1 and γX2 are measured independently from the bare hBL, and the error bars correspond to the 95% confidence interval of the Lorentzian fit.