Fig. 1: High-resolution resonant inelastic X-ray spectra of H₃LiIr₂O₆ at the Ir L₃ edge.

a (left) RIXS spectra at T = 10 K at high symmetry points of the Brillouin zone (BZ) (circular markers). The magnetic continuum extends up to 150 meV as shown in the right panel (right; data are scaled by a factor of 5). Spectra have been shifted vertically for clarity. b Sketch of the scattering geometry. The hexagonal arrangement of blue spheres represents a honeycomb layer of Ir⁴⁺ ions within the monoclinic crystal structure of H₃LiIr₂O₆. The incident (k_i) and outgoing (k_f) radiation (orange arrows) define the scattering plane (gray), with momentum transfer Q (silver arrow). Green arrows show the polarization of the X-ray electric field (π: in-plane; \(\sigma,{\sigma }^{{\prime} }\): out-of-plane for the incoming and outgoing X-ray beam, respectively). φ is the azimuthal angle defined by the crystallographic a-axis and the scattering plane. c Schematic of the extended hexagonal BZ highlighting relevant symmetry points and directions (dashed lines follow the color scheme of Fig. 3) explored in this study. L varies between 5.91 and 5.95 r.l.u. d RIXS intensity at the wavevectors of the 120° spiral order of α-Li₂IrO₃. Solid lines in (a) and (d) are fit to the data, including a Voigt profile for the elastic line (dotted black line) and a damped harmonic oscillator (gray shading) centered at E₀ = 25 meV, red bar of width 10 meV reflects the statistical uncertainty in determining E = 0 meV. All data were taken at φ = 180°.