Fig. 4: Temperature evolution of one and two triplons in (bc) polarization.

a Triplon signals in (bc) channel after subtraction of the T = 300 K spectrum. b Color plot of the subtracted triplon excitations in the T-ω plane. c Decomposition of the subtracted triplon excitations into one-triplon and two-triplon components at selected temperatures T = 4.3, 30, 65, and 120 K. d Temperature dependence of the peak energy, linewidth, and normalized intensity of the one (green inverse triangles) and two (pink circles) triplons. The triplons soften and narrow for the temperatures below T = J’ as marked by the vertical dashed line. The solid line is fit to the intensity as described in the main text. The dotted linear are guides to the eye.