Figure 2. Temperature-dependent electron–phonon coupling of the Ni-O stretch mode.

(a) Optical conductivity around the Ni-O stretching mode (open circles), for different temperatures as indicated. Lines: fit with the Fano model explained in the text. Data are offset for clarity and the shaded area indicates the difference to a constant electronic background, which was removed by subtracting the conductivity at 800 cm⁻¹. (b–d) Temperature dependence of the parameters from the Fano model fit (symbols) showing the mode frequency Ω_ph, the Fano parameter 1/q and the total linewidth Г, respectively. Solid lines: guide to the eye. Dashed line: anharmonic line broadening remaining after considering the Fano contribution (yellow area) derived from the ultrafast modulation (see text). Error bars represent the 95% confidence interval in extracting the fitting parameters and include possible uncertainties due to the background subtraction procedure (See Supplementary Methods).