Fig. 4

Scattering intensity at M point for Q = (1/2, 1/2) as a function of energy. a Three-stage energy structure composed of single-magnon excitations and two excitation continua measured at T = 1.0 K with E _i = 7.74 meV, where the scattering intensities were integrated over L. Horizontal black bars denote the energy resolution. b Energy tail of excitation continuum measured with E _i = 15.16 meV. The inset shows the excitation spectrum measured with E _i = 3.14 meV. Horizontal blue lines in a and b are background level, which was estimated from the scattering intensity between 0.12 and 0.5 meV measured with E _i = 3.14 meV as shown in the inset of b. The error of scattering intensity was calculated by the square root of absolute neutron count combined with the law of propagation of errors. The intensity and its error in this figure are given by multiplying absolute values of neutron counts and errors by the same scale factor