Extended Data Fig. 2: Magnetic excitations in LaNiO₂ at 20 K and fit of the spectra.

a, RIXS intensity map of LaNiO₂ measured with π incident photon polarization, which optimize the cross-section of the magnetic excitations. White circles correspond to the undamped mode energies of the magnetic excitation as determined from the damped harmonic oscillator function used for fitting the data. b, Intensity of the RIXS quasi-elastic line of LaNiO₂ determined from a Gaussian fit. c, Representative RIXS spectrum of LaNiO₂ (black circles) at q_// = (0.4, 0) r.l.u. and corresponding fit (red solid line). The fit function includes a Gaussian for the elastic line (orange), anti-symmetrized Lorentzian for phonon (blue) and high-energy background (dashed line) and damped harmonic oscillator function for the magnon (green). The fit function is convolved with a Gaussian with FWHM = 40 meV. d, Raw RIXS spectra of LaNiO₂ (black circles) measured with π polarization with fit superimposed (red lines).